The Portable Document Format (PDF) was developed by Adobe as a form of electronic paper. They wanted a way to simplify a Postscript document so that it could be viewed and printed on any computer system.
PDF documents are very easy to create. Basically any word-processing or drawing program can generate PDF documents by using the Print command. If the user doesn't have a tool like CutePDF installed then PDFs can be created by selecting the Postscript print driver (Apple LaserWriter), outputting to a file, loading the file in the free Ghostview program and then exporting it as PDF.
Python has excellent support for producing PDF documents using the Reportlab library.
More info on PDF is available at WikiPedia: http://en.wikipedia.org/wiki/Portable_Document_Format