YellowRose, if you have one book contracted with PA, you'll probably want to check your contract and make sure that you are free to offer the next book to another publisher. Some publishing contracts include the "right of first refusal" or "option" on subsequent books. If your contract does have this, you'll probably have to submit your second book to PA and have them reject it before you can submit it elsewhere (depending on how that clause is worded).
You do still hold the copyright to all the text in your first book, but you have licensed certain publication rights to PA, and it all depends on what rights you have licensed.
You may certainly put an intro in your second book that covers the same ideas as the intro in your first book, as long as write new text; that should be completely safe. If you want to do a cut and paste, it'll depend on your contract with PA. Did you retain the right to sell excerpts of the first book? If so, you can cut and paste. If they hold the rights for second serial rights, excerpt rights, permissions, etc, then you probably can't do a cut and paste without technically violating your contract.