I hired a developer to create an android app. The work had been done. I received myapp.apk. It's working properly.
Now, I want to to add push notifications function to the app. The developer is not available again. I did not received any source code. I just received the myapp.apk.
I found that I can extract myapp.apk. After extraction, there is a file called AndroidManifest.xml and many other files and folder.
Can I add push notifications by modifying AndroidManifest.xml file? If yes, what are further steps needed? If no, what are all possible methods to add the push notifications to myapp.apk?