Newer versions of AutoCAD (mainly 2008+) contains the capability to automatically create a DWF or PDF (added in 2010) file when you save or close your drawing.  To setup the system go to the OPTIONS dialog, then choose the |Plot and Publish| tab.  In the lower left you can turn the system on/off and control the settings.

The settings dialog allows you to designate when the publish is to take place, where the files go, etc.  Various options exist in 2010 for things like layer information, merge control, and more.