Patrick, have you tried re-installing the Reader App?
It worked! I had
no idea you could uninstall/reinstall store apps. It took me a minute to find out how to reinstall it (you have to visit the Store...), but after I reinstalled Reader, all PDFs were automatically associated and all other Store apps fixed as well.
:doh:
FWIW - MiKTeX is a LaTeX distribution. I use it to make science/math stuff, and resumes. It exports to PDF, so maybe a PDF I had was trying to reference it. Not sure, but that's likely why it wasn't working since Reader was broken and is the default PDF reader for me.
Such a simple fix that I made so difficult. Thanks everyone.
Regards,
Patrick