<?php
$pdf_list = do_shortcode('[mla_gallery post_mime_type=application/pdf link=file attachment_category=pbr orderby=meta_value order=DESC]');

echo '<ul class="list-group">';
foreach ( $pdf_list as $pdf ) {
  echo '<li class="list-group-item"><a href="' . $pdf->guid . '">' . $pdf->post_title . '</a></li>';
}
echo '</ul>';
?>

[wpcode id="6317"]