Downloading file using PHP pointer

I am storing files above the root directory of my server,
and I'm planning on giving users a download by using a php
file.

Here is my code:
For the
download link:

            href="'.FILEGRAB_ADR.'?adr='.$file.'">Download

and
for the FileGrab.php
file:

//This
            will grab a file from the server

if
            (file_exists(UPLOAD_ADR.$_GET['adr'])) {
 header('Content-Description: File
            Transfer');
 header('Content-Type: application/octet-stream');

            header('Content-Disposition: attachment;
            filename="example.CATPart"');

 header('Expires: 0');

            header('Cache-Control: must-revalidate');
 header('Pragma:
            public');
 header("Content-length: ".filesize(UPLOAD_ADR.$_GET['adr']));
            

 readfile(UPLOAD_ADR.$_GET['adr']);

            exit;
}
?>

I
got the above code (in essence) from href="http://php.net/manual/en/function.readfile.php"
rel="nofollow">here

FileGrab.php is
loading but it looks like it is just spewing out a raw text form of the file, arbitrary
text/symbols etc.

Checked that the file exists,
and file size returns a value. Don't know how to get anymore errors to check out of
it!

Does it make a difference this is a .CATPart
file, which is a little abstract but
necessary...

Any help greatly appreciated
:)