thanks for your reply. I've extended my test.
I create the pdfs with current version pdf v6 standard 318.1, then send it to my iphone and open the pdf from the apple iphone mail app. iOS ist the latest 10.0.2 version.
Attached to the message is a zip file with 11 pdf files.
With acrobat pdf version v3 - v5 it works, with the other files not.works:
If I try to open acrobat pdf version v6 - v8 with iOS Mail, then I get this screen and the mail app freezes.
I use this seetings:
Passwords are 123 and 321 (user and master)