File Explorer not previewing pdf files since 25H2 update

Paul Nicholson 560 Reputation points
2025-10-15T08:07:37.1033333+00:00

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!

Windows for home | Windows 11 | Files, folders, and storage
Answer recommended by moderator
Vivekanandan Tiwari 210 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!)
Screenshot 2025-10-20 084655

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  1. Jin Hwang 0 Reputation points
    2026-07-13T20:29:56.16+00:00

    For anyone still hitting a completely BLANK PDF preview pane (no error message, no "could harm your computer" warning - just empty) after ruling out the Mark-of-the-Web/25H2 security block and the "Show preview handlers in preview pane" checkbox fix - this may help.

    Re: the highly-upvoted answer suggesting to uncheck "Show preview handlers in preview pane" - that fix does help some people, but it's worth understanding why, because it won't help everyone. Unchecking (and often re-checking) that box forces Windows to rewrite the underlying ShowPreviewHandlers registry value. If that value was missing or in a stuck/inconsistent state, the act of toggling it can clear things up as a side effect - but the setting itself isn't what's actually broken for everyone hitting this. In my case, that checkbox was already correctly checked/enabled the entire time, verified via registry, and toggling it did nothing. So if you've tried that fix and it didn't work, don't stop there - your root cause is likely elsewhere.

    Symptoms that matched my case:

    • Preview pane shows nothing at all for PDFs (not the MOTW warning text - truly blank)
    • TXT/image previews work fine
    • New, locally-created PDFs fail too (rules out Mark-of-the-Web)
    • "Show preview handlers in preview pane" was already checked/enabled
    • Default PDF app doesn't matter - happens with Adobe or Edge set as default

    Root cause, found in two layers: (1) the preview handler CLSIDs had dropped out of the "Approved" shell extensions list, which silently blocks Explorer from loading any handler not listed there - no error, no crash, just nothing rendered; (2) even after fixing that, Adobe's own pdfprevhndlr.dll still failed to render silently (registered correctly, DLL present, correct version - just produced nothing), so I repointed the .pdf preview handler to the generic Windows PDF preview handler instead.

    Here's the PowerShell script that fixes both issues - run as Administrator:

    $fixes=@{'{DC6EFB56-9CFA-464D-8880-44885D7DC193}'='Adobe PDF Preview Handler for Vista';'{3A84F9C2-6164-485C-A7D9-4B27F8AC009E}'='PDF Preview Handler';'{8b40abb8-6c65-465a-8c4b-26224df3125f}'='Windows.Data.Pdf.ProxyStubFactory'}; foreach($c in $fixes.GetEnumerator()){$name=(Get-ItemProperty "Registry::HKEY_CLASSES_ROOT\CLSID\$($c.Key)" -Name '(default)' -ErrorAction SilentlyContinue).'(default)'; if(-not $name){$name=$c.Value}; Set-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions\Approved' -Name $c.Key -Value $name -Type String}; Set-ItemProperty -Path "Registry::HKEY_CLASSES_ROOT\.pdf\ShellEx\{8895b1c6-b41f-4c1c-a562-0d564250836f}" -Name '(default)' -Value '{3A84F9C2-6164-485C-A7D9-4B27F8AC009E}'; Stop-Process -Name explorer -Force; "RESULT:PASS DETAILS:Approved list updated, .pdf preview handler repointed to generic handler, Explorer restarted"

    What this does:

    1. Re-adds three PDF-related preview handler CLSIDs to the Approved list (they can drop out from certain updates or AV/EDR "hardening" passes)
    2. Repoints .pdf's preview handler from Adobe's (which failed silently in my case) to the generic Windows PDF preview handler
    3. Restarts Explorer so the changes take effect immediately

    If you want to check first before changing anything, here's a read-only version that just tells you PASS/FAIL on each of the three CLSIDs:

    $check=@('{DC6EFB56-9CFA-464D-8880-44885D7DC193}','{3A84F9C2-6164-485C-A7D9-4B27F8AC009E}','{8b40abb8-6c65-465a-8c4b-26224df3125f}'); $approved=Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions\Approved'; foreach($c in $check){$present=$null -ne $approved.$c;"$(if($present){'PASS'}else{'FAIL'}): $c"}

    If any come back FAIL, that's your smoking gun - run the fix script above.

    Hope this saves someone the hours of registry archaeology it took to isolate.

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  2. Pro450 15 Reputation points
    2025-10-20T03:46:36.5066667+00:00

    To shortcut or summarize some of the previous answers that work, do the following:

    1. To fix all of the future files you will download, create a text file that contains the following three lines: Windows Registry Editor Version 5.00
      [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Attachments]
      "SaveZoneInformation"=dword:00000001
      Save it and rename it ending in .reg. I called mine "Allow-Preview.reg". Double click on it.
    2. To fix the files already on your system, create another text file that contains lines similar to the following: gci -recurse "$Env:userprofile\Documents" | Unblock-File
      gci -recurse "$Env:userprofile\Desktop" | Unblock-File
      Each line would point to a folder where your existing downloaded files are located. Rename your text file ending in .ps1. I called mine "UnblockPreview.ps1". Right click on it and select "Run with Powershell". Note, you may need to disable the execution policy restriction under "System" > "For developers" > "Powershell". Make sure to re-enable it after you're done.

    Also, please note that you must be an administrator on your system to do these things. Do NOT take these lightly, especially number 1 above, because Microsoft disabled preview for a reason. You need to be sure you know that you're not downloading infected files (a difficult thing for sure).

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  3. Pro450 15 Reputation points
    2025-10-18T03:30:45.1833333+00:00

    It's probable that this change by Microsoft is because of the Rendershock malware and other malware utilizing file preview to deploy it's payload.

    But wouldn't the susceptibility to a virus be dependent on which software is set as the preview handler? Further, if the preview handler can allow a virus to deploy payload, then wouldn't the same thing be true if the file is opened (which is obviously what will happen when it can't be previewed).

    Bottom line - Isn't the correct solution to fix the preview handling programs? Or is there something in Microsoft's code prior to calling the the preview handler that is vulnerable and needs to be fixed?

    This is killing every small business person I know. Almost everyone who deals with a lot of documents depends on preview. And most small systems these days are web based, thus their documents are getting tagged as a dangerous download.

    Good Rendershock description here:

    https://www.cyfirma.com/research/rendershock-weaponizing-trust-in-file-rendering-pipelines/

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  4. Ramesh 181.2K Reputation points Volunteer Moderator
    2025-10-15T10:08:04.63+00:00

    Hi Paul,

    In that case, here are some options that I can think of.

    After saving the PDF from email to a folder, right-click on the PDF file, click Properties, select "Unblock", and click OK.

    -or-

    Create a scheduled task that executes the above PowerShell command at regular intervals to bulk unblock PDFs.

    -or-

    Create a scheduled task that executes the Streams.exe tool (from Sysinternals) at regular intervals to bulk unblock PDFs.

    Streams - Sysinternals | Microsoft Learn

    How to Bulk Unblock Files Downloaded from Internet

    Streams command-line example:

    c:\tools\streams.exe -s -d %userprofile%\downloads\

    The above command unblocks all files in the Downloads folder and subfolders.

    -or-

    Or, put all those PDFs in a FAT or exFAT partition. This may not be a feasible option for many users due to lack of security, but posting it anyway.

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