$ sudo apt-get update
$ sudo apt-get install geany-plugin-gendoc 

geany-plugin-gendoc is installed in your system.

Make ensure the geany-plugin-gendoc package were installed using the commands given below,

$ sudo dpkg-query -l | grep geany-plugin-gendoc *

You will get with geany-plugin-gendoc package name, version, architecture and description in a table

geany-plugin-gendoc package basic information: