Add taxonomies to post type page

functions.php

<?php
//* Add taxomonies to page
add_action( 'init', 'nl_add_taxonomies_to_pages' );
function nl_add_taxonomies_to_pages() {
    register_taxonomy_for_object_type( 'post_tag', 'page' );
    register_taxonomy_for_object_type( 'category', 'page' );
}