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yes you are right that apk is same format as zip. App contains ✔androidmanifest.xml it contains all permissions app requires and all action it does with package name, version … info. ✔classes.dex (dalvic cache) it is not even when app is uninstalled. only removed with root or by resetting phone. ✔asset folder contains assets (can be video for starting screen, some music, …) ✔res folder contains appearance of app with icons ✔lib contains lib which defines behaviour of app. written in hex … I don't remember it all. Everything based upon my experience not read anywhere. So, not 100% correct. I've extracted many apks and modified them as well as lowered size.