So I am thinking maybe through a form, similar to how you would do image upload, but instead of freely choosing a file from your computer to a chosen folder on the server, then saving a specific file from server to a freely chosen folder on the computer.
<form action="save.php" method="post" enctype="multipart/form-data">
<input type="file" name="fileToUpload" id="fileToUpload">
<input type="submit" value="Save File" name="submit">
</form>
<?php
if(isset($_POST["submit"])) {
//save file to chosen folder on computer.
}
?>
Kinda just like when you save a document on your computer and get to save it in any folder you choose.