The file format can now be adjusted to enable support for the XML format. DATEV writes about the ZUGFeRD format:
The ZUGFeRD format (Central User Guide Forum elektronische Rechnung Deutschland) combines the PDF invoice document with an integrated invoice file in XML format.
The Invoices can easily include XML as well. To achieve this, simply change the File Format and then click Save.

More required fields when changing the File Format: When the File Format is changed to ZUGFeRD, additional fields become mandatory. The fields will be required to be filled in during document generation.
Here is the list of all the required fields for the ZUGFeRD File Format:
| Field | API Name |
|---|---|
| Legal Entity VAT or Tax Reference | finblick__LegalEntity__c.VATID__c or finblick__LegalEntity__c.TaxReference__c |
| Legal Entity Email | finblick__LegalEntity__c.Email__c |
| Legal Entity Phone | finblick__LegalEntity__c.Phone__c |
| Legal Entity Country | finblick__LegalEntity__c.Address__CountryCode__s |
| Legal Entity City | finblick__LegalEntity__c.Address__City__s |
| Legal Entity Postal Code | finblick__LegalEntity__c.Address__PostalCode__s |
| Legal Entity IBAN | finblick__LegalEntity__c.IBAN__c |
| Invoice/Credit Note Billing Country | finblick__Invoice__c.finblick__BillingAddress__CountryCode__s finblick__CreditNote__c.finblick__BillingAddress__CountryCode__s |
| Invoice/Credit Note Email | finblick__Invoice__c.finblick__Email__c finblick__CreditNote__c.finblick__Email__c |
| Invoice/Credit Note Account Customer Number | finblick__Invoice__c.Account__r.CustomerNumber__c finblick__CreditNote__c.Account__r.CustomerNumber__c |