All you need is a PDF driver installed in Windows to PLOT to in AutoCAD, as well as the side perk of being able to Print to it from other programs like MSWord or MSExcel etc. to create PDF files too.
Free PDF drivers that work just fine in WindowsXP or higher are available through any internet search like this one, just click HERE.
If you have a problem with free, almost all of the vendors at the above link will sell you more advanced versions with more features and abilities. ◦