Maybe you can use a onchange handler on the PTNP field? Something like:
$('.PTNP label').change(function() { $('.myButton').show(); })
Add classes to your PTNP (in this example class = PTNP) and your button (in this example myButton). Set initial button style to: display: none;
I tried it out, however in my test the PTNP was not filled when uploading a file..