More than a few Songbox subscribers have asked for the ability to upload a PDF into their Songbox. Some have said this could be for lyrics while others wanted to include CD artwork while others again had mentioned production notes.
Regardless, the feature is now available.
From the Songboxes page, click "Manage":
From with the "Manage" page there is a new section that allows you attach a PDF:
Go into this section to attach your PDF:
You can also add a PDF to your Songbox when you are in the process of initially creating it. There is a new option under the "Advanced Options" section of the "Create Songbox" page.