title: Extract apk and merge with updates, then install new apk
body: <p>First of all, when you have app on your phone and this app has an update on play store, google returns only updated part of code instead of whole package (for example 3 mg instead of 8 mg that is size of whole package). I researched and figured out that on android side, google play extracts the local app and merge update file that downloaded from play store and generate new apk and then installs new apk along with update. Consider that play store doesn't have apk keystore to sign new apk, but apk gets installed successfully.
  Now, I have an application that downloads updated apk from my server. Server detects changes between two apks and returns only changes done. Now, on android side I want to my running app to extract local apk and merge it with updates and generate new apk(like play store). Also it should sign new apk but it shouldn't put my keystore in user side file.
  I recently in windows, unzipped an apk file and added some files from another apk to it. Both apks are signed. Placed that new apk in my phone. but android can't install the app and says "App cannot installed".
  How can I do this?</p>