Acrobat comes with the tools to create both XFA forms (with LiveCycle Designer) or Acroforms (directly in Acrobat). The choice may not have been clear, but it is there. They are very different technologies, with Acroforms having the most support, but with Adobe software and third-part PDF viewers.
I'm not aware of a simple way to convert from an XFA to an Acroform, though it is a bit easier with static XFAs (as opposed to dynamic).
P does stand for Portable, but that requires that someones builds a PDF viewer for your particular OS. Not every viewer supports every feature that's available with PDF. Mobile viewers in particular impose various limitations, from memory to things like JavaScript. Also, XFAs are really XML wrapped in a PDF wrapper, not really PDF at all.