for a file to upload, the forms encoding type must be set to multipart/form-data.
change the form tag:
<form action="<?php echo $editFormAction; ?>" method="post" name="WAATKRegistrationForm" id="WAATKRegistrationForm">
to:
<form action="<?php echo $editFormAction; ?>" method="post" name="WAATKRegistrationForm" enctype="multipart/form-data" id="WAATKRegistrationForm">