PDF previews not showing on File explorer preview pane when access from Shared Drive.

Hello RS,

The issue you are describing is tied to a change in how Windows 11 25H2 handles file previews in Explorer, specifically for files accessed over SMB network shares. In 23H2, the preview pane relied on the registered preview handlers (Adobe, Edge, etc.) without enforcing stricter security checks. Starting with 25H2, Microsoft hardened the preview subsystem to block certain file types from being rendered directly if they originate from network paths that are not explicitly trusted. That is why you see the failure only on 25H2 and only with PDFs on shared drives.

The preview pane uses the COM preview handler registered under HKCR.pdf\ShellEx{8895b1c6-b41f-4c1c-a562-0d564250836f}. In 25H2, Explorer now requires that the file be marked as a trusted source. Adding the path to Internet Explorer’s Trusted Sites no longer affects Explorer’s preview behavior, which is why that step did not help.

To resolve this, you need to adjust the Attachment Manager and Mark of the Web behavior for network files. In Group Policy, navigate to:

User Configuration > Administrative Templates > Windows Components > Attachment Manager

and enable Do not preserve zone information in file attachments. This prevents Explorer from tagging files from SMB shares with the “Internet” zone, which is what blocks the preview handler. After applying this policy, PDFs from network shares should preview normally.

If you prefer a registry-level change, set:

HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments

DWORD value SaveZoneInformation = 1 (disabled) or 2 (enabled). Setting it to 1 disables zone tagging and allows previews.

Another workaround is to map the network drive with the net use command and mark it as a trusted UNC path. In Group Policy:

Computer Configuration > Administrative Templates > Windows Components > Windows Explorer > Turn off security warning for UNC paths

Add your file server path there. This ensures Explorer treats the share as local and allows the preview handler to function.

This change in 25H2 is intentional from Microsoft’s side for security hardening, so the long-term resolution will likely be an update to Adobe’s preview handler or a Microsoft patch to better handle trusted UNC paths. For now, disabling zone tagging or explicitly trusting the UNC path is the supported way to restore PDF previews.

I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message. Have a nice day!

Domic Vo.

Good morning,

I hope you are doing well.

Have you found the answer useful? If everything is okay, don't forget to share your experience with the issue by accepting the answer. Should you need more information, free free to leave a message. Happy to help! :)

Domic Vo.