Thanks Milo,
File size - Yes, ginormous! I tried a 300k pdf from the same site and that wouldn't come down, whereas 300k comes down ok from other sites.
Right click - Yes, tried that, the android equivalent is long duration touch, it tried to download and failed.
Helix kindly emailed the pdf and that downloaded ok off the mail server, which may be a clue.
So I'm ok on this one but it'd be nice to sort it for future needs.
I've emailed aaib to see if they can advise.
Thanks ever so much,
Mike