It turns out, the people asking me to deliver these PDFs with a survey form have already tried IT. And, yes, IT absolutely does have a management solution -- but they have to lay hands on the iPads, to deliver the files. These are field devices, and it's time consuming and expensive to have widely scattered field teams bring in their devices, or to send someone out to visit them all.
That's why they were asking me if Survey123 could deliver the PDFs. So I let them know that, no, it cannot. Not for iPads, at least.
Thanks for all the thoughts and feedback.