Which e-mail client are you using on your phone and what OS is installed on your phone?
Have you tried downloading attachment using a different internet network?
Does that files open properly on your desktop from same e-mail?
Do you have Acrobat app installed on your Phone?
Microsoft Exchange, it's a hotmail.Com email, I'm on a note 4. Android
It does open just fine on my desktop that uses my Internet provider not cell phone network, I called the cell phone company they have no clue and can't seem to fix it
I do have acrobat
Sent via the Samsung Galaxy Note® 4, an AT&T 4G LTE smartphone
Does this happens with a emails from a specific sender?
Have you tried this with any other e-mail service...Does the issue occur with other services as well?