Unfortunately, there is no "print to PDF" app for a stock iPad. There used to be one - but it was pulled from the App Store.
If you were jailbroken, there is a tweak called TruPrint ($9.99, USD) available on Cydia (the jail breaker's app store). But, nothing stock.
If you are trying to print from a web site, you can always use the "create PDF" bookmarklet listed in this thread:
http://www.ipadforums.net/showthread.php?t=72353
Then, when offered, you can use the "Open In..." function to view the PDF (or to e-mail it from an app). But, that's the only way around it that I'm aware of. Hopefully, someone else will be along who has a better idea....
Marilyn