Ouch, that's a tough one.
If it's really a proprietary system, there's probably no chance of a converter being available.
What's the actual file format? Does it save in an an autocad format? or HPGL?
Secondly, why do you need it to be PDF? If it's for printing to a ricoh wide format, could they use a PDF print driver to drop the file into a folder for the Rioch to grab it from?