I'm a latecomer to the thread, stumbling my way here from a Google search. I found 3 of the linked solutions worked perfectly (DashCrypt, Crypt3, and jFileCrypt). Crypt3 gets my vote for combined simplicity with ability to shred original file, something the other two don't do.
Crypt3 link
I wonder why they didn't "do the trick" for muticere. Although it doesn't help with an iWork file, Microsoft Office for Mac will easily encrypt files.