Windows quietly stopped previewing your downloads. A button is coming back

Click a downloaded PDF in File Explorer with the preview pane open and, since last autumn, you get nothing useful. Not a half-drawn preview, a refusal. Enough people assumed the pane had simply broken that a lot of them stopped using it.

It wasn't broken. Windows security updates from 14 October 2025 deliberately stopped the preview pane rendering any file that carries the "mark of the web," the invisible tag Windows attaches to things that arrived through a browser, an email attachment or cloud storage. The reasoning was solid. A previewed file can contain HTML pointing at an address on another machine, and while quietly drawing that preview, Windows would reach out to the address and hand over your NTLM credentials on the way, a password-derived token offered up without a single click from you.

The cure was clumsy, though. To preview your own download you had to right-click the file, open Properties, tick Unblock, apply, and then do it again for the next one. Microsoft is now shipping the obvious middle ground. In Release Preview builds 26100.8313 and 26200.8313 the warning still appears, but there's a Preview anyway button underneath it. One click, that file only, no trip through Properties. It was first spotted in Insider notes back in April and should reach ordinary PCs over the coming weeks.

Do keep in mind what the warning is actually telling you, because that part is still useful: this file came from somewhere else. If it turned up unexpectedly, previewing it is not the moment to get curious. And if your PC never seems to receive these builds in the first place, Tendvane's Windows Update repair wizard is the cheapest thing to try before anything drastic.