Question: What does AAPT (Android Asset Packaging Tool) mean? How does it work?

Can I ship the `.so` file of one application in the APK file of another application using AAPT?

Answer: 
It is the default tool of the Android SDK to pack all classes and resources in an APK file.
When your application is compiled, AAPT generates the R class, which contains resource IDs for all the resources in your `res/` directory. For each type of resource, there is an R subclass (for example, R.drawable for all drawable resources), and for each resource of that type, there is a static integer (for example, R.drawable.icon). This integer is the resource ID that you can use to retrieve your resource. 

SOURCE: <https://developer.android.com/guide/topics/resources/accessing-resources.html> (copy/pasted)