If this is the scenario, from NopCommerce you need to call the NAV SalesOrder page that you've exposed as web service.
As an example, I report here a piece of code that comes from my book "Building ERP solutions with Microsoft Dynamics NAV". You retrieve all the orders based on the filters you want and save them on NopCommerce:
private static void ReadNAVSalesOrders()
{
//Here we have to call our NAV web service for reading Sales Orders
//Web Service instantiation
SalesOrder_Service ws = new SalesOrder_Service();
ws.Url = Properties.Settings.Default.NAVWSURL;
ws.UseDefaultCredentials = true;
//Setting filters on the table
List<SalesOrder_Filter> filterArray = new List<SalesOrder_Filter>();
SalesOrder_Filter filter = new SalesOrder_Filter();
filter.Field = SalesOrder_Fields.Sell_to_Customer_No;
filter.Criteria = "10000";
filterArray.Add(filter);
//Reading sales orders
List<SalesOrder> orderList = ws.ReadMultiple(filterArray.ToArray(), null, 0).ToList();
//Printing the results
if (orderList!=null)
{
foreach(SalesOrder order in orderList)
{
Console.WriteLine("Order No.: " + order.No);
Console.WriteLine("Order Date: " + order.Order_Date);
Console.WriteLine("----------------");
}
//Waiting user input to terminate
Console.ReadKey();
}
}
