hmtpl

I have the same issue, someone help?
Y tried that:

add_filter( 'the_content', 'my_the_content_filter', 0 );
function my_the_content_filter( $content ) {
  if (is_single()) {
  global $post;
  $pgLnk=get_post_meta($post->ID, 'Button', true);
  ob_start();
  ?>
  <div>
  ... and the rest of the html
  ... and field you want to add to content
  <?php
  $content .= ob_get_clean();
  }
  return $content;
}