How to display serial number And VAT N° in invoice

hi, i've noticed that when an user pay as a pro, there are no invoice number (but only invoice key), VATnumber, company name and adress on the invoice. But the problem is that here in EU countries, these informations are mandatory.

For the previous version of PP, there has a post on the forum to override the template in order to add these informations in it.

So can you please tell us or make a tutorial on how to add customizations for that?
Thanks