"Are there any further thoughts or suggestions?"
Yes, use the Adobe Reader, just as Mixture said
Adobe developed the PDF format in the first place, and are ahead of the others in optimising the software. Besides which, while they may try to induce you to install other software during setup, their attempts are a lot less insiduous than any other PDF reader I can think of.
However I suspect theres a bit of politicking going on ....... the latest Firefox release supposedly has native PDF reading capabilities built in, so obviating the need for a PDF reader plugin. However that doesn't allow you to read standalone PDF files - unless you want to view everything in your internet browser.....
Methinks Mozilla are just playing silly B's
PS - all PDF readers have security holes, just as all internet browsers do also.
The trick is to not open documents indiscriminately - and to disable scripting within the PDF viewer - which is enabled by default