However, PDF files that you encounter with your browser will still open in the browser. The following section covers how to make Adobe Acrobat Reader the default PDF viewer for your Edge or Chrome ...

As such, it could open a PDF file as long as the %PDF-header started within the first 1024 bytes of the file. There’s, however, a change in the scheme of things now.

Following that, go to the File Block Settings tab and make sure that the Open selected file types in Protected View setting is selected. If so, tick the Open checkbox of PDF Files.

The pdf in this thread, for example, will not open. <BR><BR>But this one will. <BR><BR>Can someone with more skill than I examine these links to determine whether there is something about the file ...

In any case, Windows 10 always sets one of these programs as the default, which means any PDF file you have will be opened with that program automatically. If you want to change your default PDF ...