I have created a simple one page PDF form using Acrobat Pro, with a few basic fields, a picture attachment field, and a submit via email field (action > mailto:email@example.com).
The form works fine on a PC. The basic fields, the attachment field, and the submit button all work correctly. However, when opened on an iPhone, only the basic fields work. The picture attachment field does not work, neither does the submit button.
I've opened it in different ways on the iPhone and tried several times. I have the actual Acrobat Reader app and also the Fill and Sign app installed on my iPhone. I've tried it different ways using those apps. Nothing I've tried works.