If You Can’t Preview Files in Windows 11, It’s Not an Error, Microsoft Disabled It on Purpose
If you’ve noticed that the File Explorer preview pane no longer works for documents downloaded from the Internet, don’t worry — it’s not a problem with your computer.
According to Windows Latest, Microsoft has disabled this feature by default in Windows 11 versions 25H2 and 24H2, and even in the latest updates for Windows 10, for an important security reason.
The preview pane is a built-in File Explorer tool that lets you see a file’s contents — such as a document, image, or code — without opening it. However, after the recent security updates, when trying to use this feature with Internet files, the system now shows a warning that the file “could harm your computer.”
A Hidden Security Risk in Windows 11
Microsoft’s decision is aimed at stopping a silent leak of NTLM credentials.
The issue was related to files marked with the Mark of the Web (MotW) tag, which is automatically applied to almost any file downloaded from the Internet — whether it’s from a browser, an email attachment, or an app like SharePoint.
When a user selected one of these files, the Windows preview handler could try to load external elements referenced in the document — such as fonts or images. If any of these pointed to a network path (UNC), Windows would automatically attempt to connect to that server, sending the user’s NTLM credentials in the process.
These credentials are encrypted authentication data derived from the Windows password, used by the operating system to prove identity to a server. By disabling the preview for these files, Microsoft effectively closes off this attack route.
How to Re-enable File Preview Safely
Although this security measure is necessary, there’s a manual way to re-enable previews.
Users can unlock each file individually by right-clicking on it, selecting Properties, and checking the “Unblock” box in the General tab.
While this makes the process less convenient, it’s also possible to unlock multiple files at once using a PowerShell command:
Unblock-File -Path "C:\Users\admin\downloads\*.pdf"
This command will unblock all files in a specific folder.
