PHP include function will parse the file. What you want to do is use file_get_contents or readfile.
Here's an example from the readfile documentation:
$file = 'somefile.gif';
if (file_exists($file)) {
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.basename($file));
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-Length: ' . filesize($file));
ob_clean();
flush();
readfile($file);
exit;
}
Change the headers to suit your particular needs. Check out the above links for more info.