Android modify APK files (decompile classes.dex)

Decompress APK file

Use 7zip to decompress the APK file (this is a ZIP compressed container)

Decompile classes.dex

Method 1: dex -> jar -> java classes

1. The file “classes.dex” can be converted to a JAR file with the following tool: dex2jar
   

   dex2jar.bat classes.dex

2. Decompress the JAR file using 7zip again.
3. Now you will get Java class files. These files you can decompile with the tool JAD.

   jad.exe -o -r -sjava -dsdrc C:/classes_dex2jar/**/*.class

Method 2: dex -> smali

To decompile and recompile the classes.dex file you can use this tool: ROMToolsPCv3

You will get smali files instead of java class files. The smali files can be modified and recompiled to classes.dex file again. How to do this you can read here: [GUIDE] Smali coding guide for beginners.