1. Teach yourself Music with a PDF file. PDF files fully support music and samples so that you can add tunes and links into PDF files, open the music in Sibelius, hear the score played. Have a look at IBegin to see what you can do.
2. Use PDF as a container. You often want to link documents together (for example your expenses claim and the receipts). PDF files allow you to embed links or the actual files and it includes lots of compression formats to squeeze the file size down to a minimum. Your content is all contained in one simple, secure self-contained format viable on any computer.
There are some ideas to start you thinking. As you can see the do far more than just documents. Do you have any unusual ways to use a PDF file?