Mobile App displays only in Preview Mode, so Payment Feature is disabled

Hello.

One of my bills comes from a company that sends a PDF with a payment feature not it.  It will not allow me to pay my bill using the app, why?  I download the invoice to my phone and open it within Adobe only to get a message I'm in preview mode and the payment function is disabled, again why?

Thank you for your help.   

**If you'd prefer questions asked in the forum vs emails, mentioning that on Google Play would be VERY helpful.  And mentioned that you can't add a question unless you sign in or create a new account would be good too.