use readfile() and application/octet-stream
headers
<?php
$handle = fopen("file.txt", "w");
fwrite($handle, "text1.....");
fclose($handle);
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename=".basename("file.txt'));
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize('file.txt'));
readfile('file.txt');
exit;
?>