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File Explorer not previewing pdf files since 25H2 update

Paul Nicholson 540 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

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  1. Ramesh Srinivasan 171.7K 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.

    1 person found this answer helpful.
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  2. Pro450 10 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/

    1 person found this answer helpful.
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  3. Joao Seabra 15 Reputation points
    2025-10-20T13:17:11.0433333+00:00

    MS should show support to the customers and send update to fix this ASAP.

    This is not productive at all for us as end users, as we need this preview function to keep staying productive at work!

    And it is not up to end users to keep trying to find solutions to issues like this!

    Thanks!

    Best regards,

    1 person found this answer helpful.
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  4. Matthew Fabilenia 5 Reputation points
    2025-10-20T17:11:45.98+00:00

    In our Windows domain environment, network file shares weren’t accessible due to this issue. It’s not practical to unblock tens of thousands of files, especially with NTFS permissions restricting who can modify zone flags.

    This bug disables file previews for Internet Zone files, and domain shares can fall into that category if the domain isn’t explicitly defined as part of the Local Intranet zone.

    The script below allows previews for Internet Zone files and adds the domain to the Local Intranet (Zone 1):

    # Allow previews for Internet Zone files
reg add "HKLM\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3" /v 180F /t REG_DWORD /d 0 /f | Out-Null
reg add "HKLM\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Lockdown_Zones\3" /v 180F /t REG_DWORD /d 0 /f | Out-Null

# Flag internal domain as Local Intranet (Zone 1)
reg add "HKLM\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap\Domains\yourdomain.local" /v "*" /t REG_DWORD /d 1 /f | Out-Null

    Run elevated and reboot.

    Yes, AI rewrote my post because I can't talk gud.

    1 person found this answer helpful.
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  5. Neil Wyatt 5 Reputation points
    2025-10-21T10:34:11.9566667+00:00

    This is a HUGE PROBLEM for me as I work in publishing and need to view literally hundreds of PDFs rapidly without waiting of Adobe to open them.

    Microsoft you have TOTALLY CROCKED my normal way of working and created me lots of extra work.

    1 person found this answer helpful.
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