This is a great question, Alison!
I was looking at the API explorer and I see that the Document Folder is an object. However, you cannot reference it from the document itself (which seems werid to me). I do know from a roadmap meeting they are trying to fix the way document folders are in the system so you should put in a feature request (I can put one in too ;) ) so the team is aware of this when they start on that proejct.
