Basic example for download a file by php
<?php$file="http://testexample.com/your_test_file.jpg"; // path to your file
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename="'.basename($file).'"');
header('Content-Length: ' . filesize($file));
readfile($file); exit;
?>
download a file by php code
OR<?php
header("Content-Transfer-Encoding: Binary");
header("Content-length: ".filesize($dest_file_path));
header('Content-Type: text/xml');
header('Content-Disposition: attachment; filename="'.$dest_file_name.'"');
readfile($dest_file_path);
?>