How to add a new Application to the Share group on galaxy S3 ?

Say that I've added my own new "text reader" App on my S3 mobile.
Whenever I need to read a text file, Android system offers some Apps to share with.

So I need to add my own new "text reader" App to this share group, can someone tell me please if its possible and how to do it.

Welcome to Android Central! I believe that's based on the code, and isn't something you can do manually.