Unable to open downloads/not able to open file

[AC Question]

I have a Motorola Maxx, running on Android. When I try to open a download, I get a message saying "unable to open". Why do I get this message, & how can I fix this?

 

[B. Diddy]

Welcome to Android Central! What exactly are you trying to download? Are you downloading files from a website using the browser? Are you trying to download a picture message in your Messaging app?