Open PDF/A files read-only.
I use Document Cloud and Adobe Acrobat Pro DC to store documents in PDF/A format. Acrobat Pro DC always warns that a file is (or claims to be) PDF/A and opens those files read-only, but Acrobat on iPhone allows me to draw over, highlight, underline, strike out, etc. a PDF/A without any warning whatsoever. The Acrobat mobile app should implement the same behavior as the desktop software when dealing with PDF/A files.