pdftk4all

The Portable Document Format (PDF) is widely accepted on the Internet in communication between different parties.

Books, papers, technical drawings, PDF is capable of handling them all. In order to make PDF a success, free (and very good) viewers are available. And some of these are even open source. Strangely enough, there is still not a good and free (open source) PDF Editor, like Adobe's Acrobat, to merge, split and annotate PDF files.