The Forms Data Format, or FDF for short, is a horrible data format thought up by Adobe. Its only redeeming feature is that in practice it's much simpler than PDF.
This Haskell package is hacked together to parse and re-serialize some files in FDF format. It certainly does not support the full range of possible FDF files. I tried to follow the specification but gave up.
The main purpose of the package is to allow parsing and serializing Canadian tax forms in FDF format. For that purpose this hack seems sufficient. If you find it doesn't work for some other FDF files, feel free to contribute some code.