If you need to create a backup of any of your apps or you simply want to keep the .APK file, App Backup Restore - Transfer is the perfect solution.
It allows you to save the APK file simply by clicking it. Then you choose what to do with the file, including sending the file via e-mail and storing it on the cloud.
Finally, the interface of the application is pretty intuitive. You'll see find a list of app icons and pick which one to store the APK file for. That's it.