You can use easier method of installation by downloading the script file and associated icons.
Put the script file in your home directory in subdirectory .pdfedit/scripts
Put the associated icons into .pdfedit/icon subdirectory in your home directory
No other installation is necessary, the function will be available next time you start the editor. If you do not want to restart editor, you can load the new functions while the editor is running by typing run("scripts/name_of_script.qs") in editor command line.

If you have root privileges, you can install this script for everybody - put the script file into /usr/local/share/pdfedit/scripts and icons into /usr/local/share/pdfedit/icon directory
(Assuming you have not changed default installation path)