Can I link to documents outside of TeamForge?

TeamForge has the concept of a 'url doc' to support this very usage.

When creating a document in TeamForge, simply choose this type from the Create screen and then enter the URL that references the document in the existing external system. This will create a 'placeholder' document in TeamForge that can be associated to, reviewed, and so on as if it were a normal document, while maintaining the document's actual contents in the external application.