Hello,
Thanks for using XStore.
Such functionality is not a part of our theme. Contact support of WooCommerce plugin first. If they sagest you to use an additional plugin, this one https://it.wordpress.org/plugins/woo-piva-codice-fiscale-e-fattura-pdf-per-italia/ or another one, but the plugin doesn’t work, contact the support of that plugin then.
Note that we do not give a guarantee for full theme compatibility with all existing 3rd party plugins.
Regards