Hi @max1114,
In order to add the order completion date, can you please try the below code in print-content.php file which is located at \woocommerce-delivery-notes\templates\print-order\print-content.php and check whether it is working fine or not.
Code:
echo date( ‘j-n-Y’, strtotime($order->get_date_completed()));
Please let us know how it goes.
Regards,
Kenil Shah