$ sudo apt-get update
$ sudo apt-get install doublecmd-gtk 

doublecmd-gtk is installed in your system.

Make ensure the doublecmd-gtk package were installed using the commands given below,

$ sudo dpkg-query -l | grep doublecmd-gtk *

You will get with doublecmd-gtk package name, version, architecture and description in a table

doublecmd-gtk package basic information: