Adobe's Portable Document Format (PDF) is a translation format used primarily for distributing files, such as documentation, across a network, or on a web site. This is an inexpensive way for CD distributors to include documentation with a CD based program or suite of programs. Files with a .pdf extension have been created in another application and then translated into .pdf files so they can be viewed by anyone, regardless of platform. The Adobe Acrobat PDF Reader software is necessary to view these files, and can be obtained free at many sites, provided by Adobe.
Read about RTF to PDF feature.