function add_protocol_header($url) {
$preg = '/^http(s)?:\\/\\/.+/';
if (preg_match($preg, $url)) {
$new_url = $url;
} else {
$new_url = 'http://' . $url;
}
return $new_url;
}
$new_url = add_protocol_header($_GET['pdf_url']);
echo file_get_contents($new_url);