This is where you enter the date of the voucher. This is the date when the invoice should be recorded in the accounting. This is usually the same as the invoice date, but you can always select another date if needed.
It is possible to determine that the invoice date should automatically be used as voucher date. If the invoice date would be changed afterwards, the voucher date would also be altered. This is determined by the setting Suggest same voucher date as invoice date, under the section Accounts Payable under the Purchase tab in the Settings procedure. If that setting is not activated, today's date will instead be used as voucher date.
You can change the voucher date on an already registered invoice even if it is final coded. If the final coding ledger has been reset (has been transferred to the accounting) the field will become grey (inactive) and cannot be modified.