Is it possible to use PHP to intercept download windows and replace them with pop-up messages?

It is not possible to directly intercept download windows using PHP as it is a server-side language and does not have control over client-side browser behavior. However, you can use JavaScript to display pop-up messages before initiating a download.

<?php
// PHP code to redirect to a page with a pop-up message before initiating download
echo "<script>alert('Click OK to start the download'); window.location.href = 'download.php';</script>";
?>