Adobe Acrobat 7.0: How To
What are PDF files? Why are they useful? When would you use them?
PDF stands for Portable Document Format; portable because unlike, for instance, Word documents, which require a copy of Microsoft Word to be purchased and installed on your system, PDFs are easily accessible for anyone who downloads and installs the free Acrobat Reader.
In addition to their portability, PDFs have a number of advantages over other document formats: