Hi,
for my client, i prepared special invoices for czech republic. But one think. Different countries have different data requirements at invoice. It would be difficult prepare module to select invoices for different groups of customers class (retail vs. wholesale) and include it in the base nopCommerce ??
Here is screen of new incoices and settings:
http://www.web-zlin.cz/images/invoice-setting.jpg
http://www.web-zlin.cz/images/invoice.pdf