So far the only way I've found is to open the document, make some trivial change, and then search the project's 'doc' directory for the file with the most recent date. I expect there is probably some really, really obvious command or it shows up in one of the info windows, maybe in the Inspector, but so far I'm blind to it.

Shoot, and now I see that someone else asked a similar question just a couple hours ago. Honestly, I searched on "file name" HERE as well, and went through a couple pages of the hits without finding something that applied. Clearly my searching skills are sub par.