http://sourceforge.net/projects/npp-plugins/files/TextFX/
While Notepad++ itself is not running:
Download and put the zip or dll file (NppTextFX.dll) inside the plugins folder nppp/plugins/
http://stackoverflow.com/questions/3958350/removing-duplicate-rows-in-notepad
Using the TextFX plugin:
TextFX->TextFX Tools->Insert Line Numbers
http://stackoverflow.com/a/14636603/362951
If
TextFX > TextFX Tools > +Sort ascending
is checked, uncheck it, then
TextFX > TextFX Tools > Sort lines case sensitive (at column)