Fix PDF Preview Error in Windows 11 25H2: ‘The File You Are Attempting to Preview Could Harm Your

If you’ve updated your PC to Windows 11 version 25H2, you might have noticed a new message in File Explorer’s preview pane when opening certain PDFs. Instead of showing a thumbnail or page preview, you see:

“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.”

Don’t panic — this isn’t an error or bug. It’s an intentional security change introduced in Windows 11 25H2. The new File Explorer PDF preview handler is stricter with security tags, meaning some downloaded or external PDFs will no longer render in the preview pane until you manually trust them.

Why Windows 11 Blocks PDF Previews Now

Windows automatically adds a small hidden attribute known as the Mark of the Web (MOTW) to files downloaded from the internet or certain network locations. This tag signals that the file might not be fully safe.

In Windows 11 version 25H2, File Explorer’s PDF preview now treats these tagged files more cautiously. When it detects a MOTW, the preview pane refuses to render the file and instead displays the new warning message.

However, you can still open the PDF normally in your preferred viewer (like Edge, Acrobat, or SumatraPDF). The block only applies to the preview pane, not to the full file access.

Quick Fix: Unblock Trusted PDFs

If you trust the source of your PDFs — for example, files you downloaded from a reputable website or received from colleagues — you can safely remove the MOTW tag to restore preview functionality.

Use PowerShell to Unblock PDFs in Bulk

You can unblock all files in a specific folder (and its subfolders) using this PowerShell command:

Get-ChildItem -Path "C:\Path\To\PDFs" -Recurse | Unblock-File

Replace C:\Path\To\PDFs with the path to your PDF folder (for example, C:\Users\YourName\Downloads).

Once done:

1. Close and reopen File Explorer.
2. Navigate back to your folder — your PDFs should now preview normally.

💡 Tip:
Run the command again on new files you download later. The MOTW tag is reapplied automatically each time you save a file from the web.

⚠️ Important:
Only unblock PDFs you fully trust. The MOTW system is a key part of Windows’ layered security and helps prevent malware from running through document exploits.

This Is Not the Same as Acrobat’s Security Warnings

Don’t confuse this File Explorer warning with Adobe Acrobat’s in-app security prompts. Acrobat may still display its own banners or alerts when a PDF tries to execute scripts, open links, or access external content.

The File Explorer message appears before any app launches — it’s handled entirely by Windows and unrelated to your PDF viewer.

If You Still See the Warning After Unblocking

If previews don’t return after following the steps above, check the following:

1. Make sure you ran the PowerShell command on the exact folder containing your PDFs.
2. Close and reopen File Explorer to refresh the preview handler.
3. Try opening the file directly in a PDF viewer to ensure it’s not corrupted.
4. Verify you’re not previewing a copy that still carries the MOTW tag.

If the file opens fine in your viewer but still won’t preview, try saving a new copy locally — this often strips leftover metadata and fixes the issue.

The Bottom Line

Your PDFs aren’t broken — Windows 11 25H2 just enforces a tighter security policy for the preview pane. The new warning is designed to protect users from potentially unsafe files, especially those downloaded from the internet.

For documents you trust, simply remove the security tag using PowerShell, and File Explorer will resume normal PDF previews — all without disabling Windows’ built-in protections.