Pyrite & Palm (IBM developerWorks). IBM developerWorks is carrying an article on using Pyrite, a set of Python tools designed to communicate with PalmOS devices. "A limitation of Pyrite Publisher is that it doesn't directly convert PDF or Postscript files to pdb files. Luckily, there is a simple workaround for this. The utility pstotext can transform a Postscript file into a text file. To generate a pdb file, first transform the ps file into a text file, and then use Pyrite Publisher to convert the text file into a pdb file."
You could convert pdf files to ps via the pdf2ps utility, then use Pyrite to convert the ps to pdb.
Abiword's File-Save As could also be used to save to pdb format.