Have ended up in a mess with PDF files & Jpeg files.
All I can manage to get with PDF files is the symbol.
Looks like I have learning ahead of me!
We all travel the same route John.
I have the same problem in Win10
It is merely what "extensions" (extension*.jpg or *.pdf)
that your software can open
I use a dinosaur 1980 ACDSee image viewer (cause I reckon its the best) but it will not open *.pdf in win10
So I used 2 differing programs to open both. jpg and pdf
I have now jumped ship to XYPlorer, which does everything, but cook my dinner.
Try the software you are using, and look for settings,
then "file associations" and add PDF
Example when I use ACDSee in W7
I had to add PDF