This condition is not unique to ÖBB.  I have seen the same with bus tickets in Sweden and (if I recall correctly) a Romanian night train.  Sure, you could argue that, with a different technical solution, they would not need this condition.  But you agreed to it when you bought the ticket.

In both cases, the information was clearly stated.  It was not hidden in hard-to-understand formulations in smallprint, so one cannot argue they are trying to mislead anybody.

There is one way in which you might get a refund, and that is if ÖBB fail to meet their part of the contract.  For example, if the train gets cancelled, you are entitled to a 100% refund, even if you have already generated the PDF.  From personal experience, customer service to get this refund could be better, so you might want to wait with generating the PDF until just before you get on the train.  Incidentally, this is true for non-refundable tickets such as saver fares as well.