I've managed to post it now, here. Many thanks for your help.

If anyone else has had problems with Acrobat's lack of intelligence about paper sizes, when printing, I hope you will upvote it

A few minutes ago I printed an A5 PDF onto 50 sheets of A5 paper. But Acrobat wasn't intelligent enough to realise it was an A5 PDF, so it scaled it up to A4. As a result half the information was missing on the printout and what was visible was huge. And I wasted an hour of my time and a lot of paper. Infuriating. One expects modern apps to be intelligent about that sort of thing, especially apps written by Adobe, who are supposed to be print experts!