[tryp4vps]

.... I didn't know about this backup method.I have to learn more about it. Can we use it to install an App which not in store anymore into another phone too ?

If your phone has an app which is not in the Play Store anymore, you may extract its apk file to sdcard storage using a backup app like this one first.

Once you get the apk file of the app, you can transfer it to another phone and install the app manually.

You do not even have to transfer it over the internet if both phones are on your hands, because you may just use bluetooth to transfer the file to another phone.