Secure file download from PHP server

< ?php
// local file that should be send to the client
$local_file = 'filename';
// filename that the user gets as default
$download_file = 'if_u_wanna_to_change_file_name_i._e._uploade_then name';
// I u do not want to change name then wrtre
//$download_file = 'if_u_wanna_to_change_file_name_i._e._uploade_then name';


// set the download rate limit (=> 20,5 kb/s)
$download_rate = 20.5;
if(file_exists($local_file) && is_file($local_file)) {
// send headers
header('Cache-control: private');
header('Content-Type: application/octet-stream');
header('Content-Length: '.filesize($local_file));
header('Content-Disposition: filename='.$download_file);

// flush content
flush();
// open file stream
$file = fopen($local_file, "r");
while(!feof($file)) {

// send the current file part to the browser
print fread($file, round($download_rate * 1024));

// flush the content to the browser
flush();

// sleep one second
sleep(1);
}

// close file stream
fclose($file);}
else {
die('Error: The file '.$local_file.' does not exist!');
}
? >