Important requirement to begin with is you need a Rooted Phone.
On a rooted Android phone, Download ES File Explorer.
If you are you are using ES File Explorer then
1. go to settings and
2 enable “Root Explorer” option to get access to root Directories.
3. Go to location address – /data/app/ here all apks are stored
This is useful if one wants to backup the installers which saves time as no need to download them again
Also, APK can can be send to other mobile phone via Bluetooth