Complex sentence: Rather than using the customer's purchase order document, an internal sales order form allows the internal audit control of completeness to be monitored as a sequential sales order number can be used by the company for its sales order documents.
Split into simpler sentences: Rather than using the customer's purchase order document, an internal sales order form allows the internal audit control of completeness to be monitored. A sequential sales order number may be used by the company for its sales order documents.