If you store your documents in CVS, Subversion, or some other SCM tool, then that tool will handle conflict resolution per its normal means.
However, if you are using the Document Manager component of TeamForge, then there is no automated means within the product to prevent another user from uploading a newer version of a given document that does not contain the changes you just uploaded. To prevent this, we recommend you use the edit lock and download lock features of TeamForge to prevent others from editing and downloading a document you are currently editing.