To open PrintMusic files, get the free FinaleNotepad program. Versions are available for Windows and Mac OS X. It opens PrintMusic files, as well as imports and exports MIDI.
To download the free program, the Finale website will require you to register a free account with them. Be sure to check the opt-in marketing settings at the bottom of the form if you don't want them to email you or give your contact information to their partners.