I was sent this link today because I think someone really wanted to start my weekend right. As if there weren't enough ways to make use of the PDF format, now here's a very simple (and quite cool) way to embed files inside a PDF and effectively hide them from the casual passer-by.
Great post from the author, and a neat little python script is posted as well - try it... it's fun!
Makes you wonder, doesn't it? What sorts of things are hidden inside the PDFs you pass around and forward?
Go read: "Embedding and Hiding Files in PDF Documents" and Didier's full blog with other interesting stuff at http://blog.didierstevens.com/.