File preview not working when file is renamed

After trialling many different combinations, the answer is that a Microsoft Update actively changes the default to "Windows PDF Previewer" in Windows Explorer. - FIX at the bottom

These are the various error's you may see in relation to the # symbol and the default Windows Previewer.

No Hash in Folder or Filename, works as expected in Windows Explorer Previewer

1 - Starting a Folder or Filename in path with a # symbol, breaks PDF Preview

3 - Putting a # symbol in the middle of the filename OR foldername, results in "File not found" within Windows Previewer

After this, I tried changing the default PDF program handler to

• Edge
• Chrome
• Adobe Reader
• Firefox

This made no difference to the previewer. Even after closing and reopening Windows Explorer.

Adobe suggests changing the default previewer through its Preferences > General > Thumbnails

https://helpx.adobe.com/acrobat/using/enable-pdf-thumbnail-preview-windows-explorer.html.

• This also didn't work.

FIX

To customise the Windows Explorer previewer, you need to edit the registry directly to overwrite Windows using - I found this solution worked immediately. https://www.nextofwindows.com/how-to-switch-pdf-preview-handler-when-one-stopped-working

Step 1 - In Regedit go to

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\PreviewHandlers

Step 2 - Copy the Value Name for the Previewer that you want to use.

• I copied the Value Name that had a data value of "Adobe PDF Preview Handler"
• You might use "Foxit PDF Previewer" or another

Step 3 - Go to

HKEY_CLASSES_ROOT.pdf\shellex{8895b1c6-b41f-4c1c-a562-0d564250836f}

Step 4 - Change the Default to the Value Name you copied in Step 2.

All Fixed!

We have a user that noticed a similar issue in our organization, and I was able to replicate it on my machine. PDF files that would normally load in the preview pane are now showing the ERR_FILE_NOT_FOUND message. I noticed that this only seems to affect PDF files with a # character in the file name. Once I removed the # character, the preview pane loaded correctly.

My laptop is using:

Windows 10 Pro

Version: 21H2

OS Build: 19044.5126

Experience: Windows Feature Pack 120.2212.4170.0

This seems to be holding for me - Thank you to Ramesh for leading me to the answer. The issue is that the Microsoft Edge Adobe Preview Handler keeps trying to take control which is why the Adobe Repair only lasts a few days at most. The 2 Reg Adds about halfway down the page worked for me and has held for 7 days - fingers crossed.

Hope this helps!

https://www.winhelponline.com/blog/pdf-preview-directory-index-file-not-found/

I made this a bit easier to run if you just like command line stuff. Just run the following for the same effect in administrator command prompt. You can add this to a batch script now as well!

reg add HKEY_CLASSES_ROOT\.pdf\shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f} /t REG_SZ /d {DC6EFB56-9CFA-464D-8880-44885D7DC193} /f