The reports so far suggest that if you have done it they can already see it on their system, based on your passport. So the need to present anything is not indicated, although it would be a good idea to have it just in case.
Obviously, you need to be connected to WiFi or mobile data, to complete the TDAC so if you download it to your phone, rather than just read it when it arrives it'll still be readable when you're not connected. (Same as any documents you have stored on your phone, like passport copies, travel insurance etc.)
But as is being said, once you've completed the TDAC it'll be on the system anyway. As an aside, I never quite understood why the SETV that one paid for wasn't automatically on the system, but one was specifically told to print that.
Actually, there is an official answer to the question on the FAQ page - looks like this