After waiting for PDFlib to be ready for 64bit Leopard, here's an alternative.
I never really liked PDFlib - bloated with a customized libtiff and not truly free - and it took a while for the authors to update it for 64bit Leopard (and then it took me a while to realize they had limited the 64bit compiling ability a little in the "Lite" version).
My early search for alternatives turned up libharu, but it was in very early development stages. Now it seems to be mature. For testing purposes, I have made a separate Haru PDF extension with a simple installation. Try it out, let me know how it works. Eventually I'll roll it into my PHP distribution.
I'll also attempt, with my limited C skills, to make MapServer use libharu for PDF support, but that could take a while (for me). I may just pass the suggestion onto the MapServer developers and hope.