Jill, stick to your guns, you are right. Acrobat is the
de facto standard for editing PDF's. Tell them Photoshop is the wrong
progamme to open a PDF with, Phototshop is for IMAGES. You don't need to export
as AI, Illustrator (from CS onwards I think, uses the PDF format for its files)
will open it, tell them to try that.
If you provided artwork that is ready for print tell them not
to mess with it, just place it in their layout software (likely to be Quark or
InDesign). Fax or email them a copy of the artwork as a bitmap so they know that
you know what it should look like and that any alterations will not be tolerated
unless you and/or your client agree to them in writing.
Best regards
Hywel Harris