Add Weight attribute in Invoice

Hi, we sell spice powders through woo commerce and use your plugin to generate invoice. Customer wants the product weightage to be displayed in the invoice.. hw can I add it..

and where can I add this functionality

add_filter('wf_pklist_add_package_product_variation', 'wt_pklist_add_meta', 10, 5);
function wt_pklist_add_meta($item_meta, $template_type, $_product, $item, $order)
{
$item_meta='Enter the item meta ';
return $item_meta;
}

to extend its features