How to prevent reverse engineering of an Android APK file to secure code?

Question

I have an app source and its APK file. Now I want to prevent this APK file from being reverse engineered. If it is possible to secure my app from reverse engineering, what a

Answer 1

Now I want to prevent this APK file from being reverse engineered.

That is impossible, sorry.

If it is possible to secure my app from reverse engineering, what are the steps to follow in my coding or any library is used for that?

ProGuard, properly configured, will obfuscate your code. DexGuard, a commercial extended version of ProGuard, may help a bit more. However, your code can still be converted into smali, and developers with reverse-engineering experience will be able to learn what you do from that smali code.

If you do not want others seeing your code, do not store that code on their device.