Hi Paul
The code is optional (you can turn off it in the configuration of the extension). The purpose of the license code is that it can be used to associal an order with user account (in case users were not logged in while making the order) .
In this case, you can make a menu item to associate order view in Documents Seller. Users can access to this menu item, fill in the code to associate the order with their account .
Hope the explanation is clear to you .
Thanks,
Tuan