for a file to upload, the forms encoding type must be set to multipart/form-data.
change the form tag to:
<form action="referral_doctor.php" method="post" enctype="multipart/form-data" name="CopperstoneDentistReferral_Copperstone_Referral" class="Copperstone_Referral" id="CopperstoneDentistReferral_Copperstone_Referral">