Those are not PDF files (they are however set up to open in Adobe Acrobat on your machine, though that application won't be able to actually read them).
VoiceAttack.dat is your profile database, the files in the "Backup" folder are backup copies saved when you made changes to your profiles.
VoiceAttack does not use .vap files to store profiles internally, those are mainly intended for exchanging profiles between users.
If you want to make a backup copy of an individual profile as a .vap file, make it the active profile, click the
icon on VoiceAttack's main window, choose "Export Profile", and follow the export procedure.
Note that profiles that you haven't created yourself may have exporting disabled.