I just created the folowing code and tested it, it works!
I added this in the file template-functions.php. This file is stored in the following map:
wp-content > themes > [name of child theme] > woocommerce > pdf > [custom map]
But I believe you can also add the code in functions.php
add_action( 'wpo_wcpdf_after_item_meta', 'wpo_wcpdf_show_product_categories', 10, 3 );
function wpo_wcpdf_show_product_categories ( $document_type, $item, $order ) {
if ($document_type == 'packing-slip') {
$locations = wp_get_object_terms ( $item['product']->get_id(), 'atum_location', array( 'fields' => 'names' ) );
$locations_list = ! empty( $locations ) ? implode( ', ', $locations ) : '–';
// get a comma separated list of categories (category links stripped)
if (isset($item['product'])) {
echo '<div class="product-categories">Locatie(s): '. $locations_list .'</div>';
}
}
}