$file_text = 'Some text here';

if (isset($_SERVER['HTTP_USER_AGENT']) and strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE'))
    Header('Content-Type: application/force-download');
else
    Header('Content-Type: application/octet-stream');

Header('Accept-Ranges: bytes');
Header('Content-Length: ' . strlen($file_text));
Header('Content-disposition: attachment; filename="downloaded_file.txt"');

echo $file_text;
exit();