Active Textbook is an interesting service that you can use to turn your PDFs into multimedia documents. The basic idea behind the service is that you can upload PDFs and add pictures, links, and videos that are displayed when students read your PDF through the Active Textbook viewer. While reading your PDF through Active Textbook students can highlight, draw, and add comments to the document.
The downside to Active Textbook is that you have to create your PDF outside of Active Textbook. You have to have the layout of your PDF set before uploading it because you can't actually change the content of the PDF, you're simply adding links to it through the Active Textbook service.
Applications for Education
Active Textbook could provide a good way to create your own short multimedia texts for students. The most compelling feature is the option for students to highlight and take notes on the document while they're reading it through Active Textbook. Active Textbook also adds a dictionary tool to your document which could be handy for some students. Active Textbook is free to use for up to 500 pages of material.