<form method='POST' action='index.php'>
<textarea cols='85' rows='15' name='persistent_notepad'>
<?php
if(!file_exists("text.txt"))
    {
    $content = fopen("text.txt",'x+');
    fclose($content);
    }
if($_POST['save'])
    {
    file_put_contents("text.txt",$_POST['persistent_notepad']);
    }

$text = file_get_contents("text.txt");
echo $text
?>
</textarea><br>
<input type='submit' name='save' value='Save'>
</form>