Load post/page through ajax WordPress

function load_page () {
   $pid = url_to_postid( $_POST['posturl'] );
   $file = null;
   global $post;
   setup_postdata( $pid ); 

   $templateLink = get_template_directory() . get_field("template_ajax_link",$pid);

   if(file_exists($templateLink)){
        $file = $template_theme_file;
   }
    echo $file;
   die();
}
add_action ( 'wp_ajax_nopriv_load_page', 'load_page' );
add_action ( 'wp_ajax_load_page', 'load_page' );

As you can see i am trying to get the a wordpress post to load through a file i have created.

Structure is like this

Ajax request is made

get post ID – done

get template directory for the file – done

get the the file contents to return to the ajax request

The file contents are like

<main role="main">
    <?php if (have_posts()): while (have_posts()) : the_post(); ?>
    <!-- section -->
        <section>

            <h1><?php the_title(); ?></h1>

        </section>
    <!-- /section -->
    <?php endwhile; ?>
    <?php endif; ?>
   </main>

As you can see the post data has to go through to the file so i can get details like the title.

Thanks