MS EXPLORER-PDF FILE PREVIEW NOT WORKING IN WINDOWS 11

Question

I know this is not a new issue, but I have tried everything and still getting the message "the file you are attempting to preview could harm your computer..." when trying to preview, yet it does allow me to open the file. It does look like Windows 11 blocked most of my PDF documents (which I was able to preview in the past), and this can be undone - unblocked, but only if I go in through 'Properties' and unblock each and every file in the directory. Is there a Windows update addressing this problem, or a way to unblock entire directories of PDF files?

Moved from: Microsoft 365 and Office | Other

Answer 1

I have a client with the problem, but there are some that work that are created by their copier/scanner. Looking at the file properties the ones that work say PDF Reader 5.0, where the ones that don't work are create with MS 365 Apps, and specify PDF Reader 8.0. This is recent, leading me to think it's a MS 365 update issue, that the Windows dev team haven't caught up with.

Answer 2

The issue you're experiencing with PDF file previews in Windows 11, where you receive a warning message about potential harm, is related to security measures that block certain files downloaded from the internet. Unfortunately, there isn't a built-in feature in Windows 11 to unblock entire directories of files at once. You would typically need to unblock each file individually through the 'Properties' dialog.

However, you can use PowerShell to unblock multiple files in a directory. The Unblock-File cmdlet allows you to remove the block from files downloaded from the internet. For example, you can run the following command in PowerShell to unblock all PDF files in a specific directory:

Get-ChildItem "C:\Path\To\Your\PDFs\*.pdf" | Unblock-File

Make sure to replace C:\Path\To\Your\PDFs\ with the actual path to your PDF files. This command will unblock all PDF files in that directory, allowing you to preview them without the warning message.

If you're looking for updates or changes in Windows that might address this issue, it's always a good idea to check for the latest Windows updates, as Microsoft periodically releases updates that may improve functionality or address known issues.

Answer 3

This isn’t a random glitch due to a recent Windows security update. Microsoft introduced stricter protection against malicious files. Files downloaded from the internet or certain network locations carry a hidden tag called Mark of the Web (MOTW). Windows now blocks previews of these files to prevent vulnerabilities in the preview pane. Opening the file is still allowed, but previewing is restricted for safety.

 

Here’s what you can try to fix it:

 

Unblock files using PowerShell (Best for multiple PDFs)

Open PowerShell as Administrator:

Search for “PowerShell” in Start, right-click, and select Run as administrator.

Run this command (replace the path with your folder):

Get-ChildItem -Path "C:\Users\YourUsername\Documents" -Recurse | Unblock-File

This removes the MOTW from all PDFs in that directory and subfolders.

Restart File Explorer and previews should work again.

Adjust security settings (Use with caution)

Go to Control Panel → Internet Options → Security tab.

Select Trusted Sites → Sites.

Add your local or network drive paths. (This reduces security, so only do it if you trust the source.)

Unblock a single file

Right-click the file → Properties → General tab.

Check Unblock under Security and click OK.

 

Let me know how it goes, Happy to help!