When I set my variable $$PicturePath to "" before, it did not clear the Web Viewer. I'm not sure what I did, but it now does what I expected. I added a Set Web Viewer script step to "Reset". That may of been it. Or maybe I simply had a typo on my variable name.
If you want to harness the power to Acrobat or another PDF editor you may just want to use the open url filewin://command and set the appropraite variables and such. We continually use PDFs and this works like a charm.