Add custom .php script?

Hey guys, long time no chat!

My client wants me to add this custom php script:

<?php
        $fh = fopen("http://driveweb.com/tech/ap/version.txt", 'r');
        $data = fgets($fh);
        $data = fgets($fh);
        fclose($fh);
        $build = trim(substr($data, 13));
?>

So that a URL I link to
(<a href="http://driveweb.com/tech/ap/<?php echo $build ?>/dw.jnlp">link goes here</a>) will automatically update based on the version specified using the $build variable.

Where should I put the custom php script within enfold? Thanks for the help!
– Julian