Hi, this is an automatic text that you have to print all reservations. What I have read here in the community all people show it as PDF on the phone, but to have it also on paper is not so bad to be sure that you have it.

Don't forget before departure to add the trip to your pass on the railplanner app to get your ticket.

Reservations and tickets are not the same.

Excellent advice to take a printout if at all possible. In the majority of cases of a mandatory reservation,  showing a PDF is OK for the inspector, but the rules for some train operators is that it must be a printout, although that is rarely implemented. However you might just get that one jobsworth official who follows the rule, and he has right on his side.

It costs nothing to print at home and if you buy from a ticket office they will give you a printed confirmation. 

One other advantage is it is easier to show a printout of your seat reservation to somebody in your seat.

In THIS train there are only RESseats so there will not be people without RES-as you cannot even enter the stazione in MIlano without. Only the odd one who mistook the carriage or did not know how the nrs work. In my recent ride on a FRecce (with printed bpaper from OeBB) well over 80% of people I could see had it on their fone)-but of course these were mostly normal pax not on pass

The QR code in the app will open the gates in Milan. No reservation needed, which is logical since there are a lot of regional trains.