$ sudo apt-get update
$ sudo apt-get install libvaladoc2 

libvaladoc2 is installed in your system.

Make ensure the libvaladoc2 package were installed using the commands given below,

$ sudo dpkg-query -l | grep libvaladoc2 *

You will get with libvaladoc2 package name, version, architecture and description in a table

libvaladoc2 package basic information: