Can I print to PDF with my iPad?
Those products didn't currently (and don't today) follow the accepted API that Apple provides for apps submitted to the App Store. Basically, Apple provides the print code and apps can't modify or extend the print function that iOS provides.

Until this changes, you will be bound to workarounds:


Jailbreak the device and look for something that enables this function.
Print to a device that will render the job as PDF. I know of Printopia that will do explicitly this. You can even control which folder on the mac gets the PDF and have it uploaded back to the phone or to a private cloud so you can get at the PDF again systematically from iOS.
Use apps that can save to PDF like Pages and many others, but this is an app feature, not built into the main print settings.