<?PHP
// We'll be outputting a PDF
header('Content-type: application/pdf');

// It will be called downloaded.pdf
header('Content-Disposition: attachment; filename="downloaded.pdf"');

// The PDF source is in original.pdf
readfile('original.pdf');
?>

或者扩展一下

<?PHP
if ( can_this_file_be_downloaded() ) {
  header('Content-type: application/pdf');
  header('Content-Disposition: attachment; filename="invoice.pdf"');
  readfile("{$_GET['filename']}.pdf");
} else {
  die("None shall pass");
}
?>