what post type are the dflip books

i am trying to implement a regular wordpress search box that will only search through dflip books. what is the post type for a dflip book?

function catalogues_search_filter($query) {
    if ( $query->is_search && !is_admin() && $query->is_main_query() && in_array('catalogues', $query->get('post_type'))) {
        // Modify the search query here
        // For example, to order the search results by title in ascending order:
        $query->set('orderby', 'title');
        $query->set('order', 'ASC');
    }
}
add_action('pre_get_posts', 'catalogues_search_filter');