It is totally possible to use the PDF, don't worry
Thank you @thibcabe for the quick reply.
OBB says
Please mind: Print ticket prior to journey!
The ticket for this journey must be printed before the journey.
I have attached a screenshot.
Can this warning be safely ignored and purchase reservations on the phone?
Thank you for your assistance.
Do we have to show the OBB pdf reservation plus Eurail day ticket to the station staff and get a proper ticket before boarding the train?
Do we have to show the OBB pdf reservation plus Eurail day ticket to the station staff and get a proper ticket before boarding the train?
No, you just board with your pass and reservation.