SmartInvoice allows you to control a desktop USB scanner using Twain. Using the Scanner selector under Tools and then the Scanner settings you can easily capture paper invoices (who still sends invoices through the mail!)
When you click the Scan button, pages from your scanner will be passed straight into SmartInvoice.
If you choose to scan on your network scanner, just choose a folder location on the network that SmartInvoice can browse to. Choose a format of PDF or Tif. Then in SmartInvoice, just click the Open button and load invoices in batches or selectively.