PDF Prototypes: Mistakenly Disregarded and Underutilized

We are all familiar with PDF documents, but I found this article in Boxes and Arrows very interesting. It has never even entered my mind to create a clickable PDF to prototype a new design concept. The article talks about adding dynamic elements to a PDF, using a PDF to mimic Ajax-like functionality to prototype a page-based application like a check out form, and including multimedia in a PDF. The author even goes on to provide the "how tos" for the reader. Check it out at http://www.boxesandarrows.com/view/pdf-prototypes. You have to scroll down the page to get to the article. It looks like the Web page isn't displaying properly. I hope you learn something new as I did.