Yes, in most cases. When you book through the DiscoverEU Travel app (via Interrail Self-Service), most seat reservations are issued as e-tickets. They're sent to you by email, and you can also find them in the app under More > Seat reservations > Your bookings.
Some trains still need a paper ticket
You'll see this when you book. Paper tickets are sent to you by post, so book early to give them time to arrive. You'll get an estimate of the delivery time, and a tracking code once your ticket is on its way.
To track your ticket:
- Use the tracking code on the PostNL website while your ticket is still in the Netherlands.
- Once it has left the Netherlands, use the same code on the website of the postal service in the country it's being sent to.
Travelling soon? If your departure is too close for a paper ticket to arrive in time, book your seat reservation at the station instead.