Pdf stands for Portable Document Format and is a popular means of transmitting and displaying information. It was developed by Adobe Systems and is supported by a free software package know as Adobe Acrobat Reader. If you are having difficulty viewing the pdf files, chances are that your computer either does not have Adobe Acrobat Reader installed, or your web browser is unaware of its presence. To rule out the second possibility, look under Start, Programs. You should see an entry starting with Acrobat. If it is there, then edit the applications preferences in your web browser to have files with the extension .pdf handled by Acrobat Reader. If you fail to find Acrobat Reader on your system, simply go to Adobe.com and download Acrobat Reader (free of charge). After installing Acrobat Reader, reboot your system, at which time your web browser should acknowledge its presence and automatically launch it when a .pdf file is encountered.