It sounds like you’re seeing a “The file you are attempting to preview could harm your computer” message when trying to preview a file. This is a common Windows/Explorer security behavior related to files downloaded from the internet or from untrusted sources. Here are practical steps you can try to resolve or work around the issue: What the message means

• Preview pane in File Explorer may block previews for files flagged with Mark of the Web (MOTW) or when a recent security update stricter metadata checks.
• This can affect common file types like PDFs, Office documents, and others, especially for files downloaded from the internet or received via email.

Safe quick checks

• Verify the file source: if it’s from a trusted source, you can proceed after unblocking the file.
• Check the file’s properties for an Unblock button (Windows): Right-click the file > Properties > if you see an Unblock checkbox or button, check/unblock it, then Apply.
• If you’re previewing a network or external drive, try copying the file to a local folder (e.g., C:\Temp) and test preview there.

Common fixes (one-time or per-file)

• Unblock the file or folder:
  • Right-click the file (or folder) > Properties > Unblock (if present) > OK.
• Unblock all files in a folder (for multiple files):
  • Use a script or PowerShell command to unblock a path, then retry the preview. If you’re not comfortable with scripting, you can perform Unblock on each file individually.
• Disable the MOTW check for a specific file type (not generally recommended for security):
  • This involves changing settings or applying a registry/workaround; consider this only if you fully understand the security implications and you’re in a controlled environment.

Preview pane settings and Windows updates

• Ensure the Preview pane is enabled in File Explorer: View > Preview pane (or Alt+P).
• Some Windows updates can affect previews. If previews suddenly stopped after an update, you might explore:
  • Rolling back a problematic update (not always advisable in production, and make sure you understand security trade-offs).
  • Checking if the issue is limited to certain file types or locations (local vs network drives).

Workarounds by file type

• PDFs: If the preview is blocked, open the PDF directly in a reader (Adobe Reader, Edge) rather than relying on the Preview pane.
• Microsoft Office documents: Office apps themselves can open the file if the preview pane is blocked; you can disable the MOTW check only if you’re in a managed environment and have explicit security policies in place.

Security considerations

• Unblocking or bypassing MOTW can expose your system to risk if the file truly is malicious. Only unblock files from trusted sources.
• If you’re on a managed PC (work device), consult IT before applying broad changes or scripts.

If you can share a bit more detail

• Which file type is causing the message (PDF, DOCX, XLSX, etc.)?
• Is this on a local drive, network drive, or external media?
• Have you recently installed a Windows update or security policy that coincided with the issue?

I can tailor steps to your exact scenario once you provide those details.