I'm on a Mac running osSierra. This Scribus newbie would appreciate some help.
Hi MarcM, welcome to the forums.
Are you trying to 'open' the pdf files or place them as pictures within a picture frame? Also which version of Scribus and Ghostscript are you using?
mnawij
Just to quickly add to what mnawij said, if you install Ghostscript after Scribus you might need to manually tell Scribus where GS is. (I think this issue is fixed on 1.5.x.)
See here https://wiki.scribus.net/canvas/OS_X_-_Installing_Scribus_on_your_Mac_the_easy_way#Installing_GhostScript_after_Scribus for instructions.