An anonymous programmer published a PDF file reader for the Sony PSP with source code.

PSPPDF is still pretty simplistic, but the base functionality of displaying text from a PDF file on the Sony PSP is working. Now the Sony PSP homebrew community is tasked to make the PDF viewer better.
More details and download on PSPUpdates.
It is surprising how many productivity programs are being developed without official developer support for the Sony PSP. See for instance the FTP client and VNC client for the Sony PSP. Maybe Sony should think of opening the PSP up for productivity software developers.
Sony is for my taste not quickly enough releasing PDA functionality for the PSP, that was mentioned a while back as something they are going to do.