There's a simpler alternative: Xpdf. If you don't want the graphical interface, then they claim that it can be compiled on any platform. PalmPDF is based on Xpdf and Palm was very much a Mac imitation.
I've been struggling for years with PDFs and I have several thousands of them.
The solution came when I started to use Acrobat 6 Pro on XP, with PDF Split And Merge and Atomic PDF Password Recovery. There was only 1 PDF that I couldn't convert to version 1.4. The others display correctly on OS 9.
When I have a new PDF, if it's version 1.6 or higher, I convert it with PDF Split And Merge to version 1.4.
Then I optimize with Acrobat 6, saving as version 1.4. Acrobat 6 is the last version that you don't have to activate online.
If it has a password, then this can be removed with Atomic PDF Password Recovery. It says that it's a demo, only converting x pages, but when you check it it converts everything.
JPEG2000 pictures cannot be viewed on OS 9. They can be converted to normal JPEG by Acrobat 6.
Another optimization is converting JBIG2 pictures to CCITT4, which will display faster on OS9.