Please download the latest versionn 4.6 from our website and try again. Revit 2015 is now a bit old, but the window should open. 

Please send us a screenshot to sales@archigrafix.com should that not work.

I downloaded the Docuflow 4.1 trial version to test it and installed it on revit 2015.

There is an icon on the revit ribbon but it doesn't seems to work. I can't even open the app window.