Once in a while one discovers a piece of software that ‘just does it right’. Pagehand, a new lean word processor, is one of these. While most applications use proprietary file formats that only they themselves can read — and maybe, if they’re nice, Spotlight and Quick Look plugins — Pagehand simply uses PDF. All necessary proprietary data used to make the file editable is saved as meta data inside the PDF structure and so you can easily send Pagehand files around and everyone can easily open, read, and print them. This is just how these things should work.
Add.: The only drawback is, of course, that you should not open these PDFs with Acrobat or Preview, edit and save them. Most applications editing PDF do not preserve third-party metadata (they should but many don’t do it) and so your editable part could be gone.