Make this plugin work in Custom Post Type?

First, I want to say thank you, this is great plugin. I think I need your help.

How to make this plugin “Add Any Extension to Pages” work in Custom Post Type?

I have custom post type “books“, I want this plugin only work for that and disable in “Page”.

I try to modify this line but still don’t work ??

if ( $wp_rewrite->using_permalinks() && $wp_rewrite->use_trailing_slashes == true && $type == 'books' ){

Can you help me, thanks!