in the code, the default file field is linked to the textfield form element:
'DefaultFileName' => "".((isset($_POST["textfield"]))?$_POST["textfield"]:"") ."",
your hidden form elemeent that contains the origianl file name is not named textfield, it is named cvv:
<input name="cvv" type="hidden" id="cvv" value="<?php echo $row_WAATKEmployment['Employment_CV_name']; ?>" />
change the default file code to:
'DefaultFileName' => "".((isset($_POST["cvv"]))?$_POST["cvv"]:"") ."",