//on test.php (for the form)
<?php

if(isset($_POST['submit']))

    include 'ajax.php';

?>
//on ajax.php
<?php

if($_SERVER['REQUEST_METHOD'] != 'POST' || !isset($_POST['submit']) || $_POST['submit'] != 'Submit'){

    exit('Invalid page request!');
}
 

$File = "mypage.html";
$Handle = fopen($File, 'a');
$Data = $_POST['name'] . " - " . $_POST['myname'] . "<br>";
fwrite($Handle, $Data);
fclose($Handle);
 $return = "Added";

echo $return;

?>