I give the answer because I need to compare 2 files in notepad++ and there is no option available.
So first enable the plugin manager as asked by question here, Then follow this step to compare 2 files which is free in this software.
1.open notepad++, go to
Plugin -> Plugin Manager -> Show Plugin Manager
2.Show the available plugin list, choose Compare and Install
3.Restart Notepad++.
http://www.technicaloverload.com/compare-two-files-using-notepad/