The Doc No field in sales order is not a mandatory field now. We are using that field to mention the customers purchase order(PO) number. Hence, any sale order cannot be made without PO number. Now it is possible to make sale orders without PO numbers.If it is marked mandatory, then it would easy for us to have a check point and avoid sale order entries without PO numbers.
Guest
If you want to implement mandatory Document Number in Sales Order, we request you to tag Manual Document Scheme Numbering in Sales Order. This will make the input mandatory for users and they can enter the value of their choice.