Zach
I think Paul misunderstood your question. Yes you can use a string (or xml value) from your actual document. You haven't provided enough details in order for us to give you the actual code update.
As an example since you are using xml mapping, you might want the contents of the first Content Control in the document to be part of the filename.
Code:
StrName = ActiveDocument.ContentControls(1).Range.Text & Format(Now, "YYYYMMDD")