This is from the Autodesk web stie and it is the way we use. It is worth getting the full version of Adobe Acrobat if you convert to PDF's often. It is quike & easy.
Create PDF files from AutoCAD® files using Adobe Acrobat® Distiller® or Acrobat PDFWriter®
Published date: 2003-06-10
ID: TS48900
Applies to:
AutoCAD® 2004
AutoCAD® 2002
AutoCAD® 2000i
AutoCAD® 2000
AutoCAD LT® 2004
AutoCAD LT® 2002
AutoCAD LT® 2000i
Issue
You would like to create PDF files from an AutoCAD® drawing.
Solution
The full Adobe Acrobat® product (not Acrobat Reader®) comes with two Windows® system drivers that can be used to create Portable Document Format (PDF) files from AutoCAD drawings: Acrobat PDFWriter® or Acrobat Distiller®.
Acrobat PDFWriter. This Windows-based system driver directly creates PDF files and will give the best results with most drawings.
Note: The Acrobat PDFWriter driver is not installed with a typical installation of Adobe Acrobat. To install the Acrobat PDFWriter system driver during the installation of Adobe Acrobat, choose a custom installation and select the Adobe PDFWriter check box.
Acrobat Distiller. This Windows-based system driver can be configured to create either PostScript (EPS) files or PDF files. If EPS files are created, Acrobat Distiller can be configured to automatically convert the EPS files into PDF files. This driver should be used only with simple drawings. For most AutoCAD drawings, better output is achieved with Acrobat PDFWriter.
Refer to the documentation provided with Adobe Acrobat and in the Adobe Support Knowledgebase for specific information about installation and configuration of these drivers.
Configuring a custom page size
The default page size for Acrobat PDFWriter and Acrobat Distiller is 8.5 x 11 inches. The available default page sizes are for smaller sheet sizes only. See Adobe Support Knowledgebase Document 322770 for information about configuring larger sheet sizes