Hello Duong,
As Bryan said, listing the order invoice via repeater or custom web part are the two easiest options in this case. First, you need to gather the data from database, for example you using a SQL data source Web part with this query:
SELECT OrderID, OrderInvoice, OrderSiteID
FROM COM_Order
WHERE OrderSiteID = '{%CurrentSite.SiteID|(identity)GlobalAdministrator%}'
ORDER BY OrderID
This will allow you to show both URL of the invoice using OrderID, and the actual HTML of the invoice, stored in OrderInvoice.
After you have setup this data source, use a Basic Repeater Web Part to list the data. You can use either this transformation to list invoice links:
<a href="~/CMSModules/Ecommerce/CMSPages/GetInvoice.aspx?orderid=<%# Eval("OrderID") %>"><%# Eval("OrderID") %></a><br />
Or this transformation, to show the actual invoices:
<%# Eval("OrderInvoice") %><br />