File Explorer not previewing pdf files since 25H2 update

Paul Nicholson 545

Since installing the 25H2 update to Windows 11, the preview for pdf files is not working.

I just get the following message "The file you are attempting to preview could harm your computer. If you trust the file and the source you received it from, open it to view its contents"

I have tried everything to restore the preview without success.

Any help would be much appreciated!

Christian Gordon 15 Reputation points

2025-10-15T13:49:18.3533333+00:00

Unfortunately, this doesn't work for me. I think it has to with the files being on a network drive.

I have tried both provided solutions.
JNels36 60 Reputation points

2025-10-15T13:59:56.7566667+00:00

This is my organizations problem too. I can preview all sorts of files that are saved and created locally but nothing from/on my network drives. Even ones I've specifically gone into the properties to check the 'unblock' box still won't allow me to preview.
Hans Schroeder 85 Reputation points

2025-10-15T16:18:03.1766667+00:00

Same here. This is completely screwing up our org's digital document workflow.
Christian Gordon 15 Reputation points

2025-10-15T19:52:16.89+00:00

Oddly, I have found that if the path is routed as a network drive (ie. Drive T:\FolderName) the preview appears to work. Not as a network path (ie. \192.168.x.x\FolderName)
Anonymous

2025-10-15T21:22:31.5866667+00:00

Same for me

I've tried all the fixes, nothing works.

I wish I hadn’t updated my system last night.
Bobby Yao 20 Reputation points

2025-10-15T21:57:15.4833333+00:00

Same issue here after running 10/15/25 update. getting same message on 99% of the files, Word, PDF, Excel, etc. Tried uninstalling/rolling back the update and ran into another error. 0x800f0825... 10/16/25 - emailed MS support regarding update uninstall error... and MS support basically went Goodfellas on me.. F U pay me. I have to now choose to pay for a support plan.

funny how this is coming up right as they end Win10 support. Unreal!
Ian McDonald 35 Reputation points

2025-10-15T22:08:44.37+00:00

I'm suffering from this too! I cannot understand why a simple update would disable the ability to preview files, which we've enjoyed for years. This is now crippling my daily work, and driving me crazy.
Randy Baroja 17,465 Reputation points Independent Advisor

2025-10-16T01:15:26.69+00:00

Hi,

Thanks for checking those already, and good call on trying the repair too.

Regards,
Accounts 55 Reputation points

2025-10-16T01:40:56.02+00:00

This is extremely frustrating and time wasting as we use the preview pane for all our pdf files. Opening each file to view it is an extreme time waster for us. Please Microsoft, give us an easy fix.
Karin Poelstra 0 Reputation points

2025-10-16T02:35:31.5+00:00

I uninstalled and no change :( ---UPDATE: Uninstalled all updates that came with the 25H2 updates on 10/15/25. Restarted and all was good. The updates re-installed overnight. Uninstalled again and turned off automatic updates. So far all good.
JM 5 Reputation points

2025-10-16T05:07:21.02+00:00

I uninstalled the update (which was installed for me on the 15/10) and it works great now. I can preview the files just fine.

My other colleagues - who were also struggling with this update - have tried the uninstall method and it has worked. It may not work for all, but it should work for most.
CrsJn 60 Reputation points

2025-10-16T06:33:58.12+00:00
Just add the path where your files are saved.

Go to Internet Options.

Go to Security Tab.

Go to Trusted sites and click sites.

Add the path where your files are saved. Make sure you uncheck the "Require server verification (https:) for all sites in this zone.

All done, go ahead and try if it works.
Paul Nicholson 545 Reputation points

2025-10-16T07:18:17.1166667+00:00

This only works for internet sites with a https:// prefix. I don't believe you can add local or network drives here...
Nurahman Soleh 0 Reputation points

2025-10-16T08:11:20.5866667+00:00

Well done, Masha Allah, it works, thank you brother.
Drewstein 0 Reputation points

2025-10-16T08:24:20.3133333+00:00

Paul Nicholson it works for me. If you type file://then your path.

my example is file://desktop-2022\users\ME\Desktop\Email attachments to rename\
Vinny N-J 0 Reputation points

2025-10-16T09:51:11.72+00:00
I was having the same issue with a customer of ours,

Their issue was when the PDF files are located in their OneDrive folder on file explorer.

If anyone is having issues with it just being PDF previews inside the OneDrive folder, what you can do is this:

Open Control Panel

Search for Internet Options

Open the Security tab

Click on Trusted Sites

Then press the "Sites" button

Then finally, add "www.onedrive.com" into the trusted sites page.

For PDFs on physical drives, it doesn't look like there is no permanent fix, but theres an answer on this forum relating to power-shell that looks like it works.
TheEntity 0 Reputation points

2025-10-16T10:40:53.5433333+00:00

Yup, similar issue with the latest update. Image files seem to appear in the preview pane, but 3d files don't show in file explorer's preview pane anymore as well as some pdf files. Note I added 3dview for Win 11 home, which worked fine until the update. Curiously zipped files with 3d files etc show fine in the preview pane when accessed.
Paul Nicholson 545 Reputation points

2025-10-16T10:55:07.89+00:00

I was getting hopeful with a couple of the suggestions.

My files are actually on a shared Teams folder synched to my OneDrive, so added both www.onedrive.com and the Teams Sharepoint path to Trusted Sites on Internet Settings.

Also added the file path as per Drewstein's suggestion in this form:

file://desktop-2022\users\ME\Desktop\Email attachments to rename\ (obvs changed for my path)

Unfortunately none of them have worked for me...😖
Neil Dixon 5 Reputation points

2025-10-16T11:51:43.9533333+00:00

Does this mean we need to ignore update from now on?

Could this mean a switch to apple?

What a pain!
JP 5 Reputation points

2025-10-16T16:06:20.0933333+00:00

I've tried the different "fixes" as well and it's nothing is working for me either. Word, Excel, and images preview - PDFs and TEXT files are NOT. This is the same issue with both local locations (i.e. on my hard drive) and on cloud based paths.
Ryan Monahan 25 Reputation points

2025-10-16T16:53:11.33+00:00

Apple has its own version of this, since there are RAMPANT issues with security these days. The entire concept of "getting things from outside your desktop" is a problem that needs to be addressed by all major players. Do not ignore updates, it's actually quite the opposite. Ensure you ARE updated.
Robert Reece 0 Reputation points

2025-10-16T16:56:41.4066667+00:00

I also UN-installed ... An hour of my life I'll never get back!

My question is, if my PC is on Auto Update, then the same issue will come up again, correct? I've never had a problem with Windows updates until today. I'd rather keep my PC up to date!
Chris Hatok 5 Reputation points

2025-10-16T17:58:40.15+00:00

I resolved this at my company. You need to put "file://" in front of any area you are trying to allow. Follow the instructions Crsjn describes but add "file://"
Cynthia Hamilton 5 Reputation points

2025-10-16T20:32:54.3366667+00:00

This worked like a "hot damn"! Thanks everyone!!
ESP IT Guy 61 Reputation points

2025-10-16T23:02:36.4733333+00:00

Cool, Microsoft deploys new "security features" with no way to manage them apart from a hacky and all out "disable security feature". Seems MS hasn't learned anything and I will continue to be baffled by their approach to anything but data mining and greed.
Anonymous

2025-10-17T01:46:06.1366667+00:00

Hello.

I have today noticed this message & I have not yet downloaded/installed 25H2.

It was discovered the Security Update for Microsoft Windows (KB5066835), installed on Oct 15, 2025 could be the culprit. I uninstalled the update & previewing .pdf's has been restored.

I hope this helps.
WINSONLOW-6332 5 Reputation points

2025-10-17T02:33:27.1666667+00:00

Has anyone found a permanent solution so far, or do we need to wait for a new Microsoft update to resolve this issue?
diman 0 Reputation points

2025-10-17T04:19:17.8433333+00:00
Go to Internet Options.

Go to Security Tab.

Go to Local Intranet

Klik Advanced

add Ip Address if file from share network

Apply
Dave N 5 Reputation points

2025-10-17T15:10:18.8066667+00:00

Adding our Shared Drive (t:) with the file:// seems to have sorted the issue. This was happening on a 24H2 and a 25H2 system, so I don't believe that it's entirely a 25H2 issue.
Diana Stefanyshin 5 Reputation points

2025-10-17T16:04:32.33+00:00

I have not yet installed the update but am getting the same message on my computer when I try to open PDF that are stored in my downloads. This is most inconvenient as I preview everything before I open it. Why is this happening since I haven't even installed the update yet>
Zara Quintana 15 Reputation points

2025-10-17T16:33:50.8933333+00:00

I use the preview option daily and this is causing me to spend more time opening and closing documents (especially pdf files). This is not good and Microsoft needs to fix it immediately. This is not a safety issue for me since I'm usually on a closed network and wouldn't open a file I'm not familiar with anyway.

Hear US Microsoft!!!! Turn this safety feature off in your next update since you are having them several times a week lately. Make it optional if someone needs it. Don't force it on all of us. I've tried clicking the unblock box on a pdf file and it still didn't work. I have thousands of files and can't spend the time to do this for everyone I need to access all day almost everyday.
Chris Black 0 Reputation points

2025-10-17T16:53:07.8766667+00:00

Just uninstall this update: KB5066835 and it will work again.
Alex Elias 0 Reputation points

2025-10-17T19:39:43.35+00:00

I am having the same issues on Windows 10 and Windows 11
Leaap-Itmair 20 Reputation points

2025-10-18T05:29:37.2433333+00:00

check my answer.
Deleted

This comment has been deleted due to a violation of our Code of Conduct. The comment was manually reported or identified through automated detection before action was taken. Please refer to our Code of Conduct for more information.
Deleted

This comment has been deleted due to a violation of our Code of Conduct. The comment was manually reported or identified through automated detection before action was taken. Please refer to our Code of Conduct for more information.
WesS-7580 0 Reputation points

2025-10-18T16:19:58.6833333+00:00

Is the removal of preview for documents with the mark of the web a mitigation for the rendershock exploit?
Júlia Alié de Vega 0 Reputation points

2025-10-18T16:38:29.1866667+00:00

Hi! I just got the solution, just download the expernal file manager, ONE COMMANDER and it’s way much much better!! And it does preview pdfs but not ms office files though

Trung Nguyễn Thành 10

Solution 1: Registry Edit (Recommended)

This procedure will configure Windows not to save zone information (Mark of the Web) for new file attachments.

⚠️ Warning: Editing the Registry incorrectly can cause system errors. Proceed with caution.

Press Win + R to open the Run dialog box.

Type regedit and press Enter. Click Yes if the User Account Control window appears.

Navigate to the following key in the Registry Editor:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies

Create a New Key:

Right-click on the Policies key, select New -> Key.

  Name the new key __`Attachments`__.
  
  __Create a New DWORD Value:__
  
     Right-click on the newly created __`Attachments`__ key, select __New__ -> __DWORD (32-bit) Value__.
     
        Name the new value __`SaveZoneInformation`__.
        
        __Modify the Value:__
        
           Double-click on __`SaveZoneInformation`__.
           
              Ensure the __`Value data`__ is set to __`1`__.
              
                 Click __OK__.
                 
                 __Close the Registry Editor__ and __Restart your computer__ to apply the changes.

After restarting, new PDF files downloaded or created should no longer trigger the preview error.

Solution 2: Disable via Group Policy Editor (Applies to Windows Pro/Enterprise only)

If you are using Windows Pro or Enterprise edition, you can achieve the same result through the Local Group Policy Editor:

Press Win + R, type gpedit.msc and press Enter.

Navigate to:

User Configuration
-> Administrative Templates
-> Windows Components
-> Attachment Manager

Find the setting "Do not preserve zone information in file attachments".

Double-click this setting and select Enabled.

Click Apply and OK.

Restart your computer to apply the changes.

Solution 1: Registry Edit (Recommended)

This procedure will configure Windows not to save zone information (Mark of the Web) for new file attachments.

⚠️ Warning: Editing the Registry incorrectly can cause system errors. Proceed with caution.

Press Win + R to open the Run dialog box.

  Type __`regedit`__ and press __Enter__. Click __Yes__ if the User Account Control window appears.
  
     Navigate to the following key in the Registry Editor:
     
     ```
     HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies
     ```
     
        __Create a New Key:__
        
              Right-click on the __`Policies`__ key, select __New__ -> __Key__.
              
                    Name the new key __`Attachments`__.
                    
                       __Create a New DWORD Value:__
                       
                             Right-click on the newly created __`Attachments`__ key, select __New__ -> __DWORD (32-bit) Value__.
                             
                                   Name the new value __`SaveZoneInformation`__.
                                   
                                      __Modify the Value:__
                                      
                                            Double-click on __`SaveZoneInformation`__.
                                            
                                                  Ensure the __`Value data`__ is set to __`1`__.
                                                  
                                                        Click __OK__.
                                                        
                                                           __Close the Registry Editor__ and __Restart your computer__ to apply the changes.
                                                           
                                                           After restarting, new PDF files downloaded or created should no longer trigger the preview error.
                                                           
                                                           Solution 2: Disable via Group Policy Editor (Applies to Windows Pro/Enterprise only)
                                                           
                                                           If you are using Windows __Pro__ or __Enterprise__ edition, you can achieve the same result through the Local Group Policy Editor:
                                                           
                                                              Press __Win + R__, type __`gpedit.msc`__ and press __Enter__.
                                                              
                                                                 Navigate to:
                                                                 
                                                                 ```
                                                                 User Configuration

-> Administrative Templates -> Windows Components -> Attachment Manager ```

                                                                    Find the setting __"Do not preserve zone information in file attachments"__.
                                                                    
                                                                       Double-click this setting and select __Enabled__.
                                                                       
                                                                          Click __Apply__ and __OK__.
                                                                          
                                                                             __Restart your computer__ to apply the changes.

HonestReviewer 15 Reputation points

2025-10-18T19:51:42.64+00:00

If you install PowerToys and activate .pdf in File Explorer add-ons, then uncheck the above in folder options, it should work
nn2 0 Reputation points

2025-10-19T03:07:15.4866667+00:00

While I was aware that Windows flagged downloaded files as unsafe I had never heard the term MoTW. Whoever slipped Mark of the Web into Microsoft's metadata lexicon is a real Beast.
IMCariño 0 Reputation points

2025-10-19T04:18:05.8533333+00:00

I ran into the same problem after the update, so I checked this feed. I'm not super into tech stuff (I didn't understand how to go about one of the answers here) but I tried clicking "Print to PDF" option while viewing the received PDF files online. I then saved it on my PC folder, closed the folder and reopened to see if it worked. Well, it did. I think the print-to-save as PDF option is bypassing any security feature that has been installed, and the system reads it as your "own" file.
hunter3740 106 Reputation points

2025-10-20T14:35:52.4966667+00:00

this worked for me (elevated ps), uninstalled recent update kb5066793, and restarted computer:

wusa /uninstall /kb:5066793

restart-computer

or also elevated ps, just recursively unblock a certain parent folder's pdf files (BUT, you'll have to redo that command with e.g. new downloads; but also note, you can just right click on any given file > properties, and at the bottom of the General tab, is the new security option, where you just check that "unblock" box):

gci c:\users\youHere\downloads -include *.pdf -recurse | unblock-file
Paul Huff 5 Reputation points

2025-10-20T16:51:50.7366667+00:00

I have the same problem and here is an interesting observation... Older pdf files dating from before about July 2022 preview without a problem.
KESHAVA SAPAAR 0 Reputation points

2025-10-20T17:56:41.0366667+00:00

use Alt+V+P at a time it enables preview pan
CARLO MATOS 0 Reputation points

2025-10-20T18:23:24.3466667+00:00

We have the same issue after the 25H2 Update.
After some troubleshooting we got around the issue by using the DNS (Server/Computer) name instead of the IP address. So instead \x.x.x.x\NetworkShare use \ServerName\NetworkShare instead. Hope this fixes the issue for you all as well.
ChrisDKD-3669 0 Reputation points

2025-10-20T19:34:06.62+00:00

I'm far from an expert, but the fix that @CrsJn provided above worked for me. I am now able to see previews of network files. The trick is to make sure you uncheck "Require server verification (https:)" before adding the local link. Then I just added file://**.myserver.mydomain
Can anyone comment as to if unchecking the Require server verification (https:) box adds much of a security risk?
DSB Designer 0 Reputation points

2025-10-21T00:06:30.0833333+00:00

Reverting to the previous install (not 25H2) reactivated the PDF display in Explorer. I figured that letting MS figure out the problem and fix it would be best. In the future I'll do a search to issues related to any upgrades before I initialize anything.
Jeff N 10 Reputation points

2025-10-21T02:17:35.4333333+00:00
I've had the same problem and believe I've found a solution.

Open Adobe Acrobat

Go to menu

Preferences

Security (enhanced)

Under 'Sandbox Protections'

UNcheck 'enable protect mode at startup'

Under 'Enchanced Security'

UNcheck 'enable enhanced security'

Select 'OK'

I hope this works for you.
Anwar Mangla 15 Reputation points

2025-10-21T03:35:32.1933333+00:00

Adding IPs to Internet Options - Trusted sites only works for files created by the same machine. Files received from others or downloaded from Internet are still getting blocked in the preview panel
Richard Simigla 0 Reputation points

2025-10-21T07:14:02.2066667+00:00

Hi,

Adding the network location to the trusted locations as file:///Z:/... worked for me (you have to disable https requirement)
Oisin Frost 10 Reputation points

2025-10-21T20:40:00.75+00:00

I rely on the Preview pane to scroll through literally hundreds of PFD drawings and other files to reference markups made. Suddenly I have to open those files individually, one by one, in a PDF viewer, and my workflow slows to a crawl. WTF????
Kodi Ebanks 0 Reputation points

2025-10-21T20:45:15.7366667+00:00

Typically, selecting "Unblock" in the file properties will resolve the issue. However, if you need to process a large number of files, it is recommended to use the Streams tool provided in the link below. You will need to either search the instructions on how to use the stream tool and let AI guide you through it

https://learn.microsoft.com/en-us/sysinternals/downloads/streams

This tool can be used to remove all "Mark of the Web" tags from your files. Doing so should resolve your issue. Additionally, please consult with your system administrator to prevent these tags from being automatically reapplied through Group Policy in the future.
Justin 0 Reputation points

2025-10-21T23:11:35.4666667+00:00

If you add the file location to the trusted sites tab in internet options, this fixes the issue. Use file://[file location]

This can also be added as a group policy to apply to all the PCs across a domain.
Oisin Frost 10 Reputation points

2025-10-21T23:19:40.51+00:00

I uninstalled 25H2 and Preview worked for 5 minutes - then stopped working again, even for PDF's that I created myself on that system. WTF??
WINSONLOW-6332 5 Reputation points

2025-10-22T00:18:05.15+00:00

I ran the command Unblock-File -Path "C:\Users\admin\Documents\*.pdf" in PowerShell, and it only temporarily resolved the issue. When the user saves new PDF files, the problem comes back again.

I would like to request Microsoft to provide a permanent fix for this issue as soon as possible.
Jess Iannone 5 Reputation points

2025-10-22T00:26:52.6666667+00:00

Here is a simple solution that worked for me -

in the file explorer, just disable this check box as shown in the image, this simply worked for me
Paul Huff 5 Reputation points

2025-10-22T11:19:45.5066667+00:00

I tried this, but unless I missed something else, it turned off all of my previews, even the ones that I had "fixed" using the "unblock" trick that I described in a previous post.
AJ Tex 0 Reputation points

2025-10-22T13:29:46.26+00:00

You should try and check your "Trust Manager" within you Pdf Viewer / Software.
Once I edited or checked my settings, all was good and back to normal.
JP 5 Reputation points

2025-10-22T16:28:07.8666667+00:00

I also tried this - but it turned off ALL previewing of files (both local and on a network).
JP 5 Reputation points

2025-10-22T16:37:03.3366667+00:00
@Jeff N your suggestion worked for my system - none of the other suggestions (and I've been following this since Oct 16th) have worked for me.

Open Adobe Acrobat

Go to menu

Preferences

Security (enhanced)

Under 'Sandbox Protections'

UNcheck 'enable protect mode at startup'

Under 'Enchanced Security'

UNcheck 'enable enhanced security'

Select 'OK'

UPDATE - Oct 24 - it worked until I restarted my laptop. Randomly, some PDFs are viewing, and others are still not. Wonky!
M_HERMAN 35 Reputation points

2025-10-22T21:10:09.79+00:00

This is an INSANE situation. I am totally on board for all things security-oriented, but perhaps not this one which is so far-reaching. I am on a STANDALONE LAPTOP and NOT ON A NETWORK. I can't even guess how many PDF files I presently have. Yes, I can call up one document, go to properties, and unblock it. But, I can't select all of the PDF files in the folder and use properties to apply unblock to all of them. We'll be on 26H2 by the time I do them al one-by-one! I'm only managing personal files, so I can't imagine how people working remotely are able to overcome this disastrous change. I see there are some solutions in the comments below, so I will give them a try. But, we should not have to "apply a solution" each and every time a new PDF document shows up and is saved on a local drive. Isn't that why we already use Defender and/or other security software products?
MIKEY Y 0 Reputation points

2025-10-23T14:59:25.29+00:00

I am not able to preview pdf files and everytime getting message - "The file you are attempting to preview could harm your computer." Please troubleshoot the problem
Sunny Surella 15 Reputation points

2025-10-24T01:13:05.54+00:00
Below solution steps worked for me:

Check if you are missing PreviewHandlers Registry Key, if yes then use below:

Method 1) Fix: Recreate the Missing PreviewHandlers Registry Key

Step 1. Open Registry Editor

Press Win + R, type regedit, and press Enter.

Navigate to:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer

Step 2. Create the Missing Key

Right-click Explorer → New → Key.

Name it exactly:
PreviewHandlers

Step 3. Restore Default Preview Handler Entries Inside PreviewHandlers, create the following String Values (REG_SZ) — you can copy and paste both the names and values exactly:

Name (Default Preview Handler)Value (CLSID)Microsoft Office Preview Handler{65235197-874B-4A07-BDC5-E65EA825B718}Microsoft Office Preview Handler{65235197-874B-4A07-BDC5-E65EA825B718}Microsoft PDF Preview Handler{DC6EFB56-9CFA-464D-8880-44885D7DC193}Microsoft Word Preview Handler{84F66100-FF7C-4fb4-B0C0-02CD7FB668FE}Microsoft Excel Preview Handler{00020827-0000-0000-C000-000000000046}Microsoft PowerPoint Preview Handler{65235197-874B-4A07-BDC5-E65EA825B718}Microsoft Outlook Mail Preview Handler{A776EDEF-81C0-4A3C-BE0A-46E36A9B8E2D}Text Preview Handler{1531d583-8375-4d3f-b5fb-d23bbd169f22}Image Preview Handler{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A} (You don’t need all of them; adding the Text, PDF, and Image handlers is usually enough.)
It should look like below screenshot:

Step 4. Restart Explorer

Either reboot, or open Command Prompt and run:

taskkill /f /im explorer.exe start explorer.exe

Then test your preview pane again. If it did not work, then use below solution as well:

I also used Mark Zuber's suggestion and used below method:

Method 2)

Automate It for Multiple Common Folders

If you want this to apply to multiple folders, use a script like this:

$folders = @( "$env:USERPROFILE\Downloads", "$env:USERPROFILE\Documents", "$env:USERPROFILE\Desktop" ) foreach ($folder in $folders) { if (Test-Path $folder) { Write-Host "Unblocking files in $folder..." Get-ChildItem -Path $folder -Recurse -ErrorAction SilentlyContinue | Unblock-File } } Write-Host "✅ All files have been unblocked successfully."

🔹 Save it as UnblockFiles.ps1, then run it once as Administrator (right-click → Run with PowerShell). This clears MOTW tags from typical folders where downloaded content lives.

I hope it will help everyone until Microsoft has a fix for it. The above may not be a proper solution, and may not work for everyone. But is a workaround for now and worked for me.
JK77 0 Reputation points

2025-10-28T11:09:16.2333333+00:00

I am also having this same issue since the update and nothing has worked. Oddly enough I can view pdfs created before the security update but not any 'newly created or downloaded' pdfs regardless of the files location. Beyond frustrating. I have spend way too long trying every fix listed in this forum to date and nothing has worked. We need a windows update to fix this - hello windows are you there?
Afshin POURHASHEMI 0 Reputation points

2025-10-28T17:15:06.6266667+00:00

J'ai le même problème mais sur Windows 10 ! Je pensais que cela venait d'Acrobat car quand je l'ai désinstallé et installé Fox It Reader à la place, mes aperçus fonctionnaient à nouveau jusqu'à ce que j'ai redémarré le PC. Depuis impossible de voir les aperçus PDF en grande taille. PAr contre Excel, Word et Jpeg fonctionnent.
Gary Nebbett 6,321 Reputation points

2025-10-31T10:10:01.4966667+00:00

Deleted (repeated information present in earlier answers).
Tina Matuszczak 0 Reputation points

2025-10-31T13:23:47.1133333+00:00

So as a temporary solution for just 1 or 2 files at a time, I have had to right click on the file - go to Properties of the file and then unblock, but this is time consuming to do for every file
Gareth Personal 10 Reputation points

2025-11-03T17:01:19.3766667+00:00

I am finding today that 3D object files, such as .obj now have the same warning and no preview even though I created them on this PC.

I have to believe at this stage its a bug.
Simon 0 Reputation points

2025-11-04T08:00:28.86+00:00

Nope not a bug, this is by design - read this and weep its permanent behaviour, Microsnot has decided we need protecting from ourselves

https://support.microsoft.com/en-us/topic/october-14-2025-kb5066835-os-builds-26200-6899-and-26100-6899-1db237d8-9f3b-4218-9515-3e0a32729685
Jainuri Atun Nisa 5 Reputation points

2025-11-06T04:30:30.6366667+00:00

I have the same problem, and for now its FIXED. You can follow this step:

https://allthings.how/fix-file-explorers-pdf-preview-warning-in-windows-11-25h2/
Daniel Smith 0 Reputation points

2025-11-06T09:25:57.8166667+00:00

Hi

This is what I received from Microsoft support regarding this issue:

This is one of the security measures applied after the October KB.

Given that authentication occurs when connecting to the remote path to ask what files exist on the target, the mere listing of files in a remote path implicitly leaks the NTLM hash to that remote path

The issue in the MSRC hardened on and after 10B.25 is that File Explorer doesn't ask a previewer to preview the contents of a downloaded file, because there’s currently no way for a previewer to convey it understands the risk of leaking NTLM hashes to remote locations and does NOT do so when previewing untrusted files.

This change addresses a security vulnerability (MSRC 98973) where NTLM hash leakage could occur when users preview unsecure files (e.g., HTML/JS) in File Explorer. The issue arises when HTML tags such as <link>, <src>, or similar attributes reference external paths, enabling attackers to exploit preview functionality. Only way is to unblock those files to remove the mark of web or copy them to a trusted folder.

Workarounds: Remove the internet security block by adding the file shares address to the Local intranet or Trusted sites security zone.

Right-click -> Properties -> Check “Unblock”.

This workaround is publicly documented under “How can I override or unblock this behavior?" in the Frequently Asked questions section of Public KB5070960: File Explorer automatically

If you are confident in the safety of both the file and its source, you may remove the internet security block.

To remove the block for a downloaded file, right-click the file in File Explorer, select Properties, and then select Unblock.

Note: The change might not take effect immediately but will be effective after the next login.

To remove the block for files on an Internet Zone file share, use the Internet Options control panel’s Security tab to add the file share’s address to either the Local intranet or Trusted sites security zone.

Warning: This configuration change will relax the security posture for all files from the listed file share.

Br

Dan
D JD 0 Reputation points

2025-11-06T17:30:31.72+00:00

Same issue here. It is so incredibly frustrating that Microsoft sees fit to create these roadblocks for us which decrease efficiency, and then fail to address the issue. I've tried every recommended fix, but the damnable preview block always turns itself back on no matter what I do. It does NOT make sense to force cloud users like myself to open EVERY SINGLE FILE EVERY SINGLE TIME if I need to read it. MICROSOFT PLEASE CORRECT THIS.
Navke 0 Reputation points

2025-11-10T12:06:22.6833333+00:00

I send the PDF files as attachment to myself and when I save the files from my mail, windows consider them to be trusted and they can be seen in preview.
Jessica Minden 0 Reputation points

2025-11-12T16:27:19.05+00:00

So instead of fixing the security whole, they just removed the ability to preview files. This was unbelievable short-sighted.
Daniel Geronimo 0 Reputation points

2025-11-13T00:28:47.58+00:00

Hi, any update?

69 answers

Mark Zuber 105 Reputation points

2025-10-15T09:35:21.4533333+00:00

Hey everyone,

Just wanted to chime in – I’ve been running into the same issue with PDF previews in File Explorer since the 25H2 update. Some PDFs show the preview just fine, but others throw this message:

"The file you are attempting to preview could harm your computer."

After digging around a bit, I realized it’s related to the Mark of the Web (MOTW). Windows tags files downloaded from the internet, and apparently the preview handler now treats those more strictly.

As a workaround, I ran this PowerShell command to unblock the files in a folder:
Get-ChildItem -Path "C:\Users\Username\Documents\PDF" -Recurse | Unblock-File

That actually fixed the preview for those PDFs – but it’s not really a proper solution. I’d rather not have to run this manually or script it every time. Would be great if Microsoft gave us a way to trust certain folders or disable this check for local files.

Anyone else found a cleaner fix?

Kind regards,
Please sign in to rate this answer.

21 people found this answer helpful.
Paul Nicholson 545 Reputation points

2025-10-15T09:53:07.1033333+00:00

Thank you Mark!

That does indeed seem to be the issue. Running that Powershell command did indeed fix the preview for the PDFs in that specific folder.

However as you say it's not really a clean solution, as I have dozens of folders with PDF's in them that are constantly being added to.

Ramesh Srinivasan 173K Reputation points Volunteer Moderator

2025-10-15T09:56:25.78+00:00

Hi Paul,

Are those PDFs downloaded from a specific site? If so, you may be able to prevent this issue by adding that site to the trusted sites list in IE options (inetcpl.cpl).

Paul Nicholson 545 Reputation points

2025-10-15T10:02:31.33+00:00

Hi Ramesh

Good advice - thanks.

Some are from specific sites, but the vast majority are received by email. It looks like all these received by email now have the preview issue.

Paul Nicholson 545 Reputation points

2025-10-15T11:28:56.5066667+00:00

That's great! Really appreciate your suggestions.

I'll probably use a combination of both a scheduled PowerShell task and the right click unblock.

It seems that the PowerShell command also works on subfolders which makes things a lot easier!

Not as easy as it was before the update though...😖

Hans Schroeder 85 Reputation points

2025-10-15T16:14:56.6066667+00:00

While this works for local file locations, it's not a solution for our situation. Our org depends heavily on using pdfs for document management. The majority are stored on network shares mapped to drives. It appears that anything stored on a network drive does not have the option in properties to "Unblock". Running the powershell command on a drive letter path errors with it saying not a valid path. Running the powershell command on the UNC path the drive is mapped to appears to complete fine, but that doesn't change the preview issue on network locations - they still get the same error.
For further troubleshooting, copying a file from a network location to a local location (I'm using C:\Temp for example), then the file does have the "Unblock" option in Properties / General. Checking the "Unblock" option doesn't fix the preview error. Running the Powershell command on the C:\Temp path fixes the error, but only after closing and re-opening explorer. In effect, this change completely screws up our workflow process.

Jimmy Madden 0 Reputation points

2025-10-15T16:20:06.85+00:00

We're finding exactly the same scenario. Network drive previews no longer work, and the file Properties doesn't have the "Unblock" option until we copy it to a local drive.

Brtpara3 10 Reputation points

2025-10-15T16:55:33.8866667+00:00

I have the same problem. All our files are on an external drive and as of today I have 0 previews on most files on the drive, not just PDFs (word, excel, outlook, and notepad at a quick glance). Preview works for some files (but I get that same error on others) on the local computer. This problem is going to make my job infinitely harder.

Express Graphics 0 Reputation points

2025-10-15T19:55:58.75+00:00

Unblocking the file through its Properties works even though there is sometimes a bit of a lag before Explorer will show the preview. However, we have hundreds of files from multiple clients stored in multiple folders across our network so this really isn't an acceptable option.

I remember a few years ago when I had to add our local network as a Trusted site to get around a similar issue were Excel always opened files that came from email in Protected Mode and I would have to click Enable Editing even though the files were saved locally to our network or the local drive.

Microsoft really has to find a better way to implement these security changes so they don't impact their users to such a degree. This has affected files that we received months ago.

Paul L 20 Reputation points

2025-10-16T09:14:30.39+00:00

This solution also worked for me, but in our case, the issue was partly due to long folder and file names—that is, the folder path plus filename exceeded the maximum allowed characters. Moving or renaming these files resolved the problem. However, there remains the issue with files marked as “Unblock” from external consultants. While the PowerShell fix addresses this, it isn’t sustainable in a production environment.

Ryan Monahan 25 Reputation points

2025-10-16T17:16:57.9366667+00:00

There will be some tweaks to this, since it's not just PDFs. I believe Microsoft is doing a good thing by being out in front of a swarm of bad things - instead of being behind and people blaming MS for NOT being secure. It is super unfortunate that every feature we use daily someone thinks of a way to weaponize it and make it do something unintended.

Ultimately what has to happen is change the metadata of the file by renaming it and opening it and then unblocking it. That works. But you are right, the MOTW is the new thumbprint on things and it's doing what its told.

Stephen S 10 Reputation points

2025-10-17T23:13:01.0666667+00:00

I finally got this fixed fully after the 25H2 update broke all my PDF previews (especially in Dropbox and on my Desktop). Unblocking individual files worked temporarily, but here’s what solved it permanently for me:

1️⃣ Remove the Mark-of-the-Web flag from all affected PDFs: Open PowerShell and run (in this example, I am unblocking ALL the files on my Desktop and ALL the files in my Dropbox):

Get-ChildItem -Path "C:\Users\<YourUserName>\Dropbox" -Filter *.pdf -Recurse | Unblock-File Get-ChildItem -Path "$env:USERPROFILE\Desktop" -Filter *.pdf -Recurse | Unblock-File

2️⃣ Tell Windows not to tag FUTURE files as “from the Internet”:

Open Registry Editor (regedit)

Go to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies

Right-click Policies → New → Key → name it Attachments

Inside Attachments, right-click → New → DWORD (32-bit) → name it SaveZoneInformation

Double-click it and set the value to 1

Close and restart your PC

After doing this, all my PDFs (local, Dropbox, and Desktop) preview normally again — no warnings, no extra steps needed.

This combination:

Unblocks existing files

Stops new ones from being flagged

Works on both local and synced folders

Hope this helps someone else — it’s been solid for me across reboots and OneDrive/Dropbox syncs! I finally got this fixed fully after the 25H2 update broke all my PDF previews (especially in Dropbox and on my Desktop).

M_HERMAN 35 Reputation points

2025-10-22T22:22:49.4+00:00

Thank you Mark!
It's a great suggestion, but I had to vote NO because it did not work for me. I ran PowerShell as an administrator. I ran the command from C:\ as "Get-ChildItem -Path "C:\Users\my-user-stuff\downloads " -Recurse | Unblock-File" but it failed to unblock my blocked PDF files. I tried it twice. No luck. But, I'll keep this advice in reserve just in case.

Chakraborty, Arnab (India) 5 Reputation points

2025-10-28T07:45:13.49+00:00

Try to add the network drive(Files that you try to access) "\ccc\cc\cc"
And click to add (uncheck the Require server verification)

Which will help you preview the PDF files without any issues

Stefan Jaronski 0 Reputation points

2025-10-31T22:04:32.52+00:00

It worked! I download scientific literature PDF files into my Downloads folder for renaming and filing. Renaming because most such files have an alphanumeric file name totally unrelated to the article title. I entered
Get-ChildItem -Path "C:\Users\thebu\downloads" -Recurse | Unblock-File

the C drive direction being specific to my computer.

Jamie Stephenson 0 Reputation points

2025-11-01T14:25:46.4533333+00:00

Firstly: Thanks for the script, it worked for existing files in the folder.
I am on Windows 10 with the recent update and had PDF files in a folder some previewing, some not. Prior to the update they all previewed. The ones "not" were blocked, but unblocking via the Properties screen did not enable preview, despite appearing to unblock. Unblocking via the script did unblock, so it looks like the Properties method is incomplete since the recent update. I am not clear whether the issue is with the unblocking or some new restriction placed on PDF files.

Alberto Pinho 0 Reputation points

2025-11-05T10:00:09.9933333+00:00

O mesmo acontece comigo W11 25H2. Mas não são todos os arquivos. Uns são pre visualizados e outros não, com a mensagem "O arquivo que você está tentando visualizar pode danificar seu computador. Se você confia no arquivo e na fonte de onde o recebeu, abra-o para visualizar o conteúdo." No meu Lap Top com W11 24H2 todos são pre visualizados.

Peter 5 Reputation points

2025-11-11T12:31:13.0933333+00:00

Just to do a variation on this, I open the specific folder (in explorer) I want to unblock and "Open in Terminal" (PowerShell) then use the below:

Get-ChildItem -Path ".\" -Recurse -Filter "*.pdf" | Unblock-File

I like these PowerShell Unblock-File options over the Internet Security and Registry options as I don't want to just open a blanket security hole that this update closed.

(I saw another comment that added the filter to keep it more limited)
Sign in to comment

Use comments to ask for clarification, additional information, or improvements to the question.
R B 110 Reputation points

2025-10-16T01:56:57.3666667+00:00

Problem Solved!! I un-installed the 25H2 updates and everything works GREAT!!
Please sign in to rate this answer.

18 people found this answer helpful.
Deleted

This comment has been deleted due to a violation of our Code of Conduct. The comment was manually reported or identified through automated detection before action was taken. Please refer to our Code of Conduct for more information.

Neil Dixon 5 Reputation points

2025-10-16T15:27:52.85+00:00

The same worked for me, surely such a mega organisation has a Quality Control procedure that should capture this sort of thing?

rosm2004 20 Reputation points

2025-10-17T14:18:17.83+00:00

I tried adding the local path for my files as outlined by CrsJn (thank you), but it tells me that I can't have wildcards (*). I don't have any wildcards. It appears it only accepts internet paths. These files are on OneDrive, so I signed onto OneDrive and added the path for the parent folder. Tried previewing the files - I can preview PDFs in the parent folder but not in the subfolders. When I tried adding a subfolder to trusted sites, it tells me it's already in the trusted zone. Very frustrating.

Stratos Kouzounis 0 Reputation points

2025-10-20T07:27:25.1266667+00:00

Not in all files, check again please — I did that too, and yes it fixed most of them, but I still have the problem in some.

Oisin Frost 10 Reputation points

2025-10-21T20:09:40.4933333+00:00

Yep uninstalled 25H2 updates and now Preview is operational. WTF Microsoft???

Mark Staples 0 Reputation points

2025-10-24T16:13:44.7533333+00:00

This worked for me, thanks.

Soren H 10 Reputation points

2025-10-27T14:03:45.2766667+00:00

I reported this as a bug to Microsoft: https://learn.microsoft.com/en-us/windows-insider/feedback-hub/feedback-hub-app

Alberto Pinho 0 Reputation points

2025-11-05T10:02:25.0566667+00:00

Respeito sua decisão, mas acho que vou aguardar uma atualização da MS.
Sign in to comment

Use comments to ask for clarification, additional information, or improvements to the question.
Striver 75 Reputation points

2025-10-16T01:38:26.39+00:00

Work-around: Use Microsoft Power Toys to preview.

Install Microsoft's free Power Toys, which has many other great features. Installation is quick and easy.

To preview a file in File Explorer, highlight the file. Then Ctrl + Space. Preview pops up.

Works for most kinds of files.
Please sign in to rate this answer.

15 people found this answer helpful.
Accounts 55 Reputation points

2025-10-16T02:00:30.6033333+00:00

Thanks for the tip this is great, but I'm hoping Microsoft fix this issue in the next update. Judging by the comments, it's an inconvenience no one is happy with.

Prox-Zero 0 Reputation points

2025-10-16T16:17:42.05+00:00

So far this has been a solid work around

Patrick Flynn 0 Reputation points

2025-10-16T18:31:39.8233333+00:00

Thank you, this worked great, and I'll use it until MS fixes their problem! If you notice that WORD docs don't preview in the Outlook app, then try "WORD edit in browser" to view the doc before downloading it.

laurum 0 Reputation points

2025-10-17T23:25:38.7266667+00:00

That is genius! I already have it installed for other uses but I love it for that too!!

Rui Vasco Oliveira 0 Reputation points

2025-10-22T15:20:31.0566667+00:00

The Power Toys PDF preview is missing important information for organizers. It doesn't display the number of pages and buttons to jump between pages.

M_HERMAN 35 Reputation points

2025-10-22T21:13:39.4966667+00:00

This is a great suggestion, but if I am casually perusing a folder looking for something in a PDF, I want to preview it right then and there in explorer, not do ctrl-space and get a new popup window for each one.
But, THANKS for teaching me a new trick!

M_HERMAN 35 Reputation points

2025-10-23T18:56:12.1366667+00:00

Let me just clarify: If I am looking through a year's worth of monthly statements in PDF form, and I'm trying to find one particular item (and I know approximately where it would be found in any of those documents) I want to use PREVIEW in that folder to do my task. I don't want to open each and every one in Adobe, and I don't want the individual PowerToys display in separate windows, etc. etc. I love all of the suggestions I've seen already, but none work. I'm reticent to un-install 25H2 at the moment, but starting to lean in that direction. But at some point it will need to be installed and then we'll be back where we started.

Joyce R 0 Reputation points

2025-10-28T17:20:56.44+00:00

doesn't work for zip files

Clyde Clark 5 Reputation points

2025-10-29T21:29:22.0733333+00:00

Thanks for this tip. The issue was killing our workflow. The implementation of security theater by MS is still lame, but it is nice to have a workaround a ctrl-space away.

Blair Collins 5 Reputation points

2025-10-31T14:50:26.4766667+00:00

I can't get the Powertoys to work. When I press Ctrl - Space the preview pane says "Select a file to preview" even though I had already selected the file in file explorer. I've turned on the PDF preview pane setting in the powertoys and done a reboot of the computer in between. Anyone else seeing this behaviour? The space bar peek feature of Powertoys works for me but not the preview pane.

Dale S 0 Reputation points

2025-10-31T18:01:00.4433333+00:00

This is the way. Powertoys gave me an effective work-around.

Nic J Shodire 0 Reputation points

2025-11-03T17:58:54.76+00:00

Blair Collins, I'm having the same issue. It seems that whatever is keeping PDFs from being previewed by default in explorer is also preventing it from working even with powertoys.
Ctrl + Space is for the Peek feature in powertoys, so it isn't going to affect the preview pane. It will open a new window.
Sign in to comment

Use comments to ask for clarification, additional information, or improvements to the question.
Vivekanandan Tiwari 75 Reputation points

2025-10-20T03:18:02.11+00:00

Here is a simple solution that worked for me -

in the file explorer, just disable this check box as shown in the image, this simply worked for me

(This happened on windows 10 as well!)
Please sign in to rate this answer.

15 people found this answer helpful.
María Soledad Lanfranconi 45 Reputation points

2025-10-20T13:07:53.2066667+00:00

that option just stop preview from working at all for me, at least on win 11

Evan S. Tallas 0 Reputation points

2025-10-25T01:04:19.8133333+00:00

This worked for me in Windows 11 Latest Developer preview. Thx!

Arttu Kärpinlehto 1 Reputation point

2025-10-25T19:12:50.4133333+00:00

It's entirely counterintuitive, but this also worked for me (Windows 10 22H2 with KB5066791). I do have PowerToys installed so perhaps disabling the builtin previewer allows PowerToys handler to work.

menotu 0 Reputation points

2025-10-31T08:54:25.5666667+00:00

Worked for me too and I also have PowerToys installed.

Olivopuccino 0 Reputation points

2025-11-02T07:01:45.2833333+00:00

Well done ! Works on Windows 11 pro 25h2 latest build 26200.7019

CG 0 Reputation points

2025-11-05T15:50:53.77+00:00

This is the way.

Paul Nicholson 545 Reputation points

2025-11-05T16:02:13.8166667+00:00

Wow - it works! Tried everything else suggested and this is the only thing that has worked. I was resigned to have to manually unlock every new file I added, but no need for this now. Many thanks! 👍

Sandra King 0 Reputation points

2025-11-06T14:18:53.14+00:00

I can't see the screenshot?

Star Photo 0 Reputation points

2025-11-07T17:12:46.3633333+00:00

This fixed it for me. Thanks!

Marie Shively 0 Reputation points

2025-11-08T19:33:49.4766667+00:00

Finally, an answer that actually works! Thank you so much!

Muhammad Siddiq Abdul Rashid 0 Reputation points

2025-11-11T03:35:44.02+00:00

This is the best! Works for me!
Sign in to comment

Use comments to ask for clarification, additional information, or improvements to the question.
Anonymous

2025-10-17T02:13:01.54+00:00

Hello.

I have today noticed this message & I have not yet downloaded/installed 25H2.

It was discovered the Security Update for Microsoft Windows (KB5066835), installed on Oct 15, 2025 could be the culprit. I uninstalled the update & previewing .pdf's has been restored.

Still running 24H2.

I hope this helps.
Please sign in to rate this answer.

13 people found this answer helpful.
Chris Black 0 Reputation points

2025-10-17T15:24:03.38+00:00

Yes, this was the culprit for me.

KEVIN 0 Reputation points

2025-10-19T17:15:11.7233333+00:00

I am on 25H2 but this solution also worked for it has also stopped all my pdf's from being yellow another issue I have been trying to resolve thank you very much all the other solutions of using Powershell etc only work until you next download a file.

Erica Gardner 21 Reputation points

2025-10-20T13:11:57.73+00:00

I also uninstalled KB5066835 and it fixed my problem.

Stockland and Trantham Law Firm 5 Reputation points

2025-10-20T14:55:09.52+00:00

I have tried to uninstall KB5066835 but it is not listed as an option to uninstall for me. Is there a workaround?

Karin Poelstra 10 Reputation points

2025-10-20T15:36:29.11+00:00

Has Microsoft weighed in on this? Not seeing any response from them.

Stefan Blom 319.9K Reputation points MVP Volunteer Moderator

2025-10-20T16:45:08.5233333+00:00

@Karin, Microsoft do not read these forums for feedback or error reports. You can send feedback in the Windows feedback hub (see https://support.microsoft.com/en-us/windows/send-feedback-to-microsoft-with-the-feedback-hub-app-f59187f8-8739-22d6-ba93-f66612949332).

Bonar Gultom 0 Reputation points

2025-10-21T03:49:29.44+00:00

In my case, I uninstalled KB5066835 and it fixed my problem.

Michael Woods 0 Reputation points

2025-10-21T11:45:56.1766667+00:00

Worked for me too. Thank you. Now going to report this to Microsoft via Stefan's link above

M_HERMAN 35 Reputation points

2025-10-22T21:19:41.0433333+00:00

Just as Stockland and Trantham Law Firm reported above, this update is NOT AVAILABLE to be uninstalled.
And, I will use Stefan's link above as well.

Jess Iannone 5 Reputation points

2025-10-22T23:09:47.2366667+00:00

In Windows Explorer folder options, View Tab, uncheck "Show preview handlers in preview pane" should fix the issue

María Soledad Lanfranconi 45 Reputation points

2025-10-23T12:29:20.92+00:00

Jess that disables preview altogether for me

M_HERMAN 35 Reputation points

2025-10-23T18:16:00.33+00:00

Jess, I WANT and NEED to see the previews for the workflows that I use. For me, this would be like powering down the whole device.

Kathy T 0 Reputation points

2025-10-24T18:18:36.32+00:00

Still running 24H2 but uninstalling KB5066835 worked for me.

Wilpete 0 Reputation points

2025-10-28T11:14:12.0533333+00:00

Same for me. Reverted security which is not exciting thing to do. Worked. Will keep checking for a Microsoft update.
Sign in to comment

Use comments to ask for clarification, additional information, or improvements to the question.

Share via

File Explorer not previewing pdf files since 25H2 update

69 answers

Your answer