generating pdf documents with PDF, missing FPDI

Hello,

with PHP I often generating PDF documents with the FPDF library. This
library is ported to Rails and work fine for my tasks until now.
Now I have to edit and extends some PDF master drafts with some text.
Under PHP I using FPDI for this task. Now I can't find a port of FPDI to
Ruby.

Anybody know an other gem for editing PDF master drafts?

If no, can anybody help me, porting FPDI to Rails? I'm not new in Rails,
but my knowlegde about creating a library, gem or port to Rails is very
poor. Is there a good instruction for that?

Thanks, Daniel