Please be advised that Microsoft is disabling auto preview of files downloaded from the internet in File Explorer.

This is a security measure designed to stop exploitations and attack routes automatically running when files such as PDFs (which can contrain scripts and links) are automatically previewed (which is similar to automatically opening the file).

Preview functionality will be disabled by default for all files marked as originating from the web. If you see the following message in File Explorer then you are seeing this new behaviour: 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.

If you are confident in the safety of both the file and its source, you can remove the internet security block – right-click the file in File Explorer, select ‘Properties’, and then select ‘Unblock’. We have also had reports that if you manually open a file fully (eg double click it) then it will auto preview in future when you revisit that file.