Categories and Tags in Pages

By the default categories and tags are enabled to Posts only.

To enable in Page you can use this code snippet.

You can add it on your Functions.php or use any code snippet plugin that supports php blocks such as Scripts Organizer.

<?php

function register_category_and_tag_with_pages(){
  /*add categories and tags to pages*/
  register_taxonomy_for_object_type('category', 'page');
  register_taxonomy_for_object_type('post_tag', 'page');
}
add_action( 'init', 'register_category_and_tag_with_pages');

function register_pre_get_category_and_tag_with_pages( $query ) {

  if ( is_admin() || ! $query->is_main_query() ) {
    return;
  }
  /*view categories and tags archive pages */
  if($query->is_category && $query->is_main_query()){
    $query->set('post_type', array( 'post', 'page'));
  }
  if($query->is_tag && $query->is_main_query()){
    $query->set('post_type', array( 'post', 'page'));
  }
}
add_action( 'pre_get_posts', 'register_pre_get_category_and_tag_with_pages');