Yes, that should be no problem. Paper or mobile pass doesn't make a difference.

Thanks. Finding it impossible to do electronic my. So as long as the Station Booking offices issue them. Then great. Cheers 

Hi all, I had the same question. Because what we are worried about, is that the trains will them be fully booked.

We arrive on 17th of juli in Bucharest. Will we be able to reserve a (night)train sleeping compartment to Budapest/Vienna/Prague for the 1st of August still do you think?

Thanks!

Bucharest to Vienna can be booked online (stops even in Budapest but arrives pretty early) :D 
There is no Nighttrain from Bucarest to Prague either you go via Budapest or via Vienna

Bucharest - Budapest cant be booked online but should be able from International Ticket offices eg. DB Reisezentrum or their Hotline. 

You may consider the Brasov to Budapest Nighttrain called “Corona”  (catch a daytrain from Bucharest to Budapest) as this Nighttrain have a good dinning carriage the whole Journey