The DB App is great. It lets you buy tickets, informs you of delays and possible alternatives especially if you miss your connection, you can file a request for a refund, you can reserve a seat, you can use the comfort check-in and check yourself in, so you wouldn't have to show your ticket. You can even request a refund up to two hours after you purchased your ticket, without any fees.

No PDFs or print-outs or forms are needed.

Yes, you still get a PDF ticket sent to your email, but you aren't required to use it.