Your invoicing program has a file called customer.dbf which contains your customers' names and addresses. It includes fields for Bill To (the fields that start with "BT") and Ship To (the fields that start with "ST").
In order to bring your customer information into another application, you need to import the customer.dbf file into the other application.
You can find the customer.dbf file in your main program directory for your Invoicing program:
C:\Program Files\MySoftware\MyInvoices\