Aha, I found some info
here.
From a really quick scan, my guess is that (in the context of Sony and iRex owners) it's a gui application that uses the MS Word binaries to convert from any format that MS Word can read (like HTML, rtf, txt) into a pdf that is formatted to work on Sony Reader or Iliad. I didn't notice if the appropriate settings were clear in that thread or not, but am I close?