Cannot preview pdf files in Windows Explorer

jtweeks

I recently have been prevented from previewing pdf files on Windows Explorer - receiving 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."

Could this be resolved with a Bitdefender setting or do I need to look elsewhere?

I subscribe to Bitdefender Total Security and I'm running on Windows 11.

AlFifi_Defender

Hi @jtweeks

Thanks for raising this — that warning message is actually a built-in part of Windows 11’s Preview Pane security, not necessarily triggered by Bitdefender. However, Bitdefender can indirectly affect the behavior if certain modules are active.

Here are a few things you can try:

🛠 Suggested Fixes:

1. Temporarily disable the Preview Pane:
   
   • Open Windows Explorer → Click View → Show → Uncheck Preview Pane.
   • Then re-enable it and test again.
2. 
   
3. Check Bitdefender’s Advanced Threat Defense:
   
   • Go to Bitdefender app → Protection → Advanced Threat Defense.
   • Try disabling it briefly (for testing only) to see if it impacts PDF previews.
4. 
   
5. Ensure your default PDF previewer is not blocked:
   
   • Make sure Adobe Reader or your default PDF app is properly registered as the preview handler.
   • You may also try repairing Adobe from Control Panel.

If this persists, I’d recommend checking Windows Defender’s App & Browser Control, as well as any recent Windows security updates that might have tightened preview behaviors.

Let us know how it goes!

— AlFifi_Defender 🇸🇦

“Together we shield smarter.