To retrieve an invoices that have not yet been closed, go to Acquisitions ⇒ Invoices.
You can retrieve all open invoices (Invoice – Closed Date ⇒ Does Not Exist) and find the invoice(s) you are looking for in the list by using the following default search. If the Retrieve Results Immediately box is checked, a result list will populate immediately upon going to the Invoice Search tab.
OR You can search for a specific invoice by changing the dropdown from Invoice - Closed Date to Invoice - Vendor Invoice ID and searching for the invoice number in your paper invoice.
In the results grid, click on the blue Vendor Invoice Id link to retrieve the invoice you want to process.
For more information on invoices see Invoice Overview