PHP Decode

if (!empty($_REQUEST['affid']) && !empty($_REQUEST['u']) && !empty($_REQUEST['rebrand-report'])) {
    $affid = $_REQUEST['affid'];
    $path = $_REQUEST['u'];
    $filename = basename($path);
    $filename = !empty($filename) ? $filename : "rebrand.pdf";
    header("Pragma: public");
    header("Expires: 0");
    header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
    header("Cache-Control: public");
    header("Content-Description: File Transfer");
    header("Content-Type: application/pdf");
    header("Content-Disposition: attachment; filename=$filename");
    header("Content-Transfer-Encoding: binary");
    $file_get_contents = file_get_contents($path); 
    $regex = "#xxx-?[0-9a-zA-Z]+xxx#";
    $content = preg_replace($regex, $affid, $file_get_contents);
    echo $content;
    exit;
}