Reading some of the other posts, it looks like the most recent version of PCStitch Pro is supposed to be able to open the .pvf files. Would that be version 9, or should 8 be able to open it as well?
I've got PCStitchPro 8.003.08, and it won't open Pattern Viewer files. The really strange thing - I installed Pattern Viewer to print out a pattern that wasn't in a .pat format, and now I can't use either the PCStitch Symbols OR PCStitch Symbols 2 font libraries. Looking through the files, the files are still there, but they appear to have had all information removed from them.
The PCStitch symbol fonts are in with the other fonts. When you install PatternViewer, it "steals" the .pat extension from PCStitch and is reluctant to give it up.
I suggest you try to update PCStitch Pro. If there is no update available try this (warning, it's scary but save).
Go to the Add/Remove (Program Updates in Vista) Select PCStitch Pro as if you are going to remove it. As soon as you get a confirmation prompt, cancel it (click cancel).
The software will have maintenance applied which should correct the font problem and will reset the "owner" of the .pat extension.