External php file that can hook into Wordpress (+ Advanced Custom Fields) functions

externalWpFunctions.php

<?php 

  include('wp-load.php');

  $post = get_post(2);
  setup_postdata( $post );

?>

  <h3><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h3>
  <span>Post Object Custom Field: <?php the_field('map_location'); ?></span>

<?php
  wp_reset_postdata();
?>