I don't use their program, and almost never use Calibre. I use Windows to drag-and-drop files into my SD card. It reads rtf, but not doc; I've been caught out on the train, going to open a file I *know* I loaded, and then realizing I must not have grabbed the rtf version. (RTFs show up as whatever I've put in the Properties field for title, or by filename if I've left it blank.)

Huh. Firmware weirdness, I suppose.