Microsoft told Windows Latest that it disabled the File Explorer Preview pane in Windows 11 25H2 and 24H2 for internet downloaded files. If you create a file locally, you can still preview it, but File Explorer Preview won’t work for files downloaded from the internet due to security reasons. This change is even live in Windows 10 with its last update.
For those unaware, File Explorer has two panes by default. When you click on ‘View,’ it lets you toggle between Details and Preview. While the Details pane gives a brief breakdown of file information, such as the author of the file, creation time & date, the Preview Pane lets you quickly preview the file’s content without opening it.
You just need to select the document, and its preview will automatically appear on the right side of File Explorer. Other file formats, such as .docx and even .py (Python), are also supported.
However, File Explorer now shows the following error when you try to preview files downloaded from the internet or a remote network:
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.
Why does the File Explorer Preview Pane no longer work for some files?
Microsoft disabled File Explorer previews for Internet-downloaded files to stop a quiet NTLM hash leak.
Specifically, if a file has been marked as “Mark of the Web (MotW),” it’ll be blocked. For those unaware, a file has a Mark of the Web (MotW) tag when it’s downloaded from the following sources:
- random internet websites.
- apps like SharePoint.
- email attachments.
- Mostly anything downloaded using a browser like Edge or Chrome
When you select a downloaded file, the Windows preview handler inside File Explorer may load things it references, such as images, fonts, etc. If any of those points to a UNC path (like \\server\…\windows.png) or a file: URL, Windows can reach out over SMB during the preview and send NTLM credentials.
What are NTLM credentials?
Microsoft has now turned off the preview feature in File Explorer for downloaded files to block this path. Unfortunately, this change also affects consumers, not just enterprise customers.
“Starting with Windows security updates released on and after October 14, 2025, File Explorer automatically disables the preview feature for files downloaded from the internet,” Microsoft told Windows Latest in a statement. “If you are confident in the safety of both the file and its source, you may remove the internet security block.”
How to unblock previews in File Explorer
If you trust the file, you just need to right-click the file in Explorer, select Properties, and check ‘Unblock’ under the security section.
While it’s a simple workaround, it still defeats the whole purpose of ‘quickly‘ previewing files in Explorer. If you need to click four times to see a preview, you might as well open the file, which would not take more than two clicks. However, thankfully, there’s a PowerShell script that lets you unblock all files in a specific path.
In PowerShell, you just need to run the following command:
Unblock-File -Path "C:\Users\admin\downloads\*.pdf"
It will unblock all .pdf files in the downloads folder, including those you plan to download in the future. As long as you trust what you download, this should be good to go. You can run the same script for other paths or file types.
This change is rolling out as part of Windows October 2025 Patch Tuesday, which is the same update that broke WinRE (Windows Recovery Environment) and even LocalHost.
