Fix Adobe Acrobat Reader could not open PDF because it is either not a supported file type or because the file has been damaged error on PC.

You can allow or block Microsoft Edge from opening PDF files externally by changing some settings using Registry Editor or Group Policy Editor in Windows 11/10.

I use PDF Exchange Viewer for opening pdf's. Problem in Firefox is that clicking a link that should open the pdf in the viewer returns an error message from the viewer software.