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.
After the last tutorial on how to download sheet music files there were some requests on how to upload files to the site for other readers to see.
If you've transcribed some music from Halo or any other Bungie or Wideload game and would like to share it with the community here through Rampancy's sheet music section, first you need to have an account, confirm that account, and be logged in. All of those steps are covered in the tutorial on How To Download Sheet Music Files. After you've followed those steps, come back here.