Do you see a message like this when you try to open the PDF document?
If so, it is a special type of PDF form called "dynamic XFA" authored with Adobe LiveCycle Designer.
The Acrobat Reader mobile apps (for iOS, Android, Windows Phone) do not support XFA forms.
Please download the PDF document to your Windows or Mac computer and open it with the desktop version of Acrobat Reader DC.
Please let us know if you have a different problem.