Q: Android: installing non-Google Play apk with different signature from the Google Play one My question is about the case when an app is published on Google Play as a demo, but it is also distributed on a web-site:
1-with another developer signature 
2-with no signature.
I would like to know if when installing from outside Google Play (case 1 & 2) the app will overwrite the old demo app, provided the user gave permission to install non-Google Play apps.

A: 
with no signature

Unsigned APKs cannot be installed. 

if when installing from outside Google Play (case 1 & 2) the app will overwrite the old demo app

No, because the signatures will not match. The installation will simply fail.
