Simple PDF manipulation

Let's say I have a complicated PDF document, like a Christmas card, that was made in Illustrator -- too complicated to easily create from scratch using PDFlib. Is there a way to use PHP make simple text changes - like changing "Dear XXX" to "Dear John"? I've opened the files with a text editor and cannot locate the simple text, it appears to be encoded somehow. The PDF has no security or encryption in it. Thanks....