1 - Through the complete receipt of a purchase order. In this way, all lines from a purchase order are considered 'Received' and the purchase order is automatically closed after this posting.
2 - Through manually posting received products. Once RetailVista determines that all lines of a purchase order have been received, a question will be asked whether the purchase order can be closed.
There is a task 11497 to expand this functionality so that it is built into a lower level in Retail3000. It will no longer matter whether it is manually posted, for example through an EDI packing slip, or even through the complete receipt of a purchase order. Once all lines of a purchase order have been received, Retail3000 will automatically proceed to close the purchase order.