Add the customer's VAT Number to the invoices. Print

To add the customer's VAT Number to their invoices for legal purposes in the EU and some other countries, you can do so by going to: /components/invoice_templates/default_invoice/default_invoice_pdf.php

And adding the following line:

if(!empty($this->invoice->client->settings['tax_id']))
    $address .= $this->invoice->client->settings['tax_id'] . "\n";

Please note this will be overwritten on update.

Thanks to Paul13 on the Blesta forums for this tutorial.