The WWF has released a file format (and associated free software for the Mac with a Windows version to follow soon) that cannot be printed. Apparently, the file format is technically very similar to the pdf format but the print option is completely blocked.
The format was developed to stop documents being printed out unnecessarily and is intended to help create a new awareness about the use of paper.
WWF documents can be opened with most programs that can open pdfs. The WWF format and software are free for everyone, including organisations.