The WWF file format, in case you missed reading about it before, is just a regular PDF file except that you can’t print the content of that document. This format was developed by WWF Germany to prevent unnecessary printing.
You may download the WWF software for free from SaveAsWWF.com and it’s now available for both Mac and Windows machines.
The WWF software will install as a virtual PDF printer and you can then convert documents or emails to the WWF format by simply printing them with this new printer.
Once installed, the software will also associate the .wwf extension with the default PDF reader on your machine but if you are sending that file to someone else who may not have the WWF software, just change the extension from .wwf to .pdf and they won’t even notice the difference – see example.