I've got ThinkFree Office installed too. I wish I had known that before I shelled out $15 for DocumentsToGo. Oh well. I was thinking maybe it was like Google Earth and Google Books where you could go into the market and update it(i.e., it was already "purchased") but it still wants me to pay $15 for it... I'm going to download the free version and see what happens.
EDIT: I was thinking maybe ThinkFree Office worked like DocumentsToGo did, where you could download the free version, then install a full key and it would unlock, but it doesn't appear to work that way... The Lite version still appears as Lite.
EDIT 2: Apparently it's not the full version either. I opened a .rtf and tried to edit it and it prompted me to buy the full version... It'd be nice if I could remove it since I already have DocumentsToGo, but I'm thinking the second best course of action would just to forget that it's there.