Silly thought, but if you need a PDF reader, why not use Adobe Reader for free?
https://get.adobe.com/uk/reader/ I would be weary of installing something 'from another company' that is proving to be this troublesome. If their activation process is triggering false positives in antivirus software, isn't this perhaps an indication of something being off....
On the other hand, the standard Windows 10 defenses are quite thorough these days, so you could temporarily switch from BitDefender to Windows' own Defender and see if that helps.