Corrupt or damaged file

[#1]

This document can not be opened because it is corrupted or damaged.   

How do I resolve this issue?   It works fine from a pc,  only occurs on my phone. 

[#2]

I have the same problem. PDF files attached to emails are fine, but every time I download a file from the web, I cannot open it. Adobe says the file is damaged or corrupt. No problem when using my laptop for the same file.