What is the universal Document format on the Macintosh? (format you can be sure any Mac can display)? I'm preparing a document for Macintosh users.
Currently the document is in .doc format.

Will all Mac OSX users be able to view that format?
If not, is there a better universal format to use? (.RTF, .PDF, etc.)
PDFs will open in Preview for viewing - no Adobe Reader required. RTF will open in TextEdit, and can be edited, also with no optional software required. Which one is better depends on whether you want the user to be able to edit the document, or just read it.