Thanks for the tip,
I know this thread has been stale for a while but I just realized I had not followed up on this.
I guess what I was originally looking for was a quick introduction to document types for dummies so to speak. I have been working on learning Java and so I think I am starting to get it. I was getting confused thinking that document types were directly related to file types. (wt.epm.document and wt.document etc.. confused me.)