When using electronic invoices you can save up to 70% of cost. Invoices that are transmitted by electronic means will be accepted by the EU member states under the precondition, that the authenticity and origin of its contents are guaranteed. This can be achieved by advanced digital signatures. A member state, however, can require that the signature is based on a qualified certificate and processed by a secure signature creation device. Another option is to use EDI.

PDF is a widely used format for such electronic invoices. A PDF invoice containing a digital signature that has been created by a smartcard and a (qualified) certificate will meet the legal requirements. Also mass signatures are accepted by financial institutions.