I want to create a reference number for every Magento order that comes, which I want to use for courier billing purposes. A reference number will be additional security for me for courier billing purposes. I want to use both order number and reference on shipping slip.
Not sure why this redundancy is needed but you may identify an order by both order id or order increment id. They are different.
Besides from that an additional attribute for order entity can always be created with an install/setup script
$attribute = array( 'type' => 'text', 'backend_type' => 'text', 'frontend_input' => 'text', 'is_user_defined' => true, 'label' => 'reference', 'visible' => true, 'required' => false, 'user_defined' => false, 'searchable' => false, 'filterable' => false, 'comparable' => false, 'default' => '' ); $installer->addAttribute('order', 'custom_reference', $attribute);
or is the question more about dragging attribute data over to a shipping slip?