automatic printing

Here's a product that will do just that:

http://www.ornic.com/add-ins/exlife.shtml

(there are no spaces in the URL)

You will have to define a rule, and How to define it depends on your mail client.
Regardles of how, you will need to have associated the .pdf file to the Acrobat reader or any other Acrobat Reader like aplication.
With groupwise for example you can define a rule to match the subjet or the sender of the email, and then issue a "send to" the attached file to the printer.