Hi OlgaHelena
We cannot give you an example as customisations are out of the scope of our support service, but we can give you some tips, so you can code it yourself.
If you inspect the PO's PDF template, you'll see how the item's product is being obtained (in line 98):
$product = Helpers::get_atum_product( $item->get_product() );
Once you get the product there, you can get any meta from it using the WC_Product object getters or in the WP way, just using the get_post_meta() function.
I hope this helps.
Best Regards,
Salva.