How to extract data from an .APK file? I want to extract or copy every detail that .apk contain, like for example extracting data from whatsapp.apk or linked-in.apk or twitter.apk.

Please note that I dont want to extract my personal data from any installed app on my phone instead I want extract the data and images which the app developer had added while making the app.
As suggested earlier, Apktool is a good option, 

Requirements:


Java Runtime Environment
Windows wrapper script (Right click, Save Link As apktool.bat)
Apktool.jar


(For Linux and Mac OS the files and installation instructions are also available:  Installation for Apktool)

Usage

Copy the apktool.bat and apktool.jar files to a folder preferably with no spaces eg inside the  C:\ directory. (e.g C:\Apktool)


Open command prompt by pressing shift and right click simultaneously.
In the command prompt type apktool d [apkname.apk] (e.g apktool d WhatsApp)
Find the extracted apk in the folder with the apk name (in this case (C:\Apktool\WhatsApp)
You can now browse through the folder to find all resources of the app e.g manifest.xml and PNG images in res folder or doing a search.


Acknowledgements: 

Apktool a tool for reverse engineering