Reports, including invoices, are generated in Open Document Format, which can be opened in numerous spreadsheet applications, as outlined here: http://opendocumentfellowship.com/applications. The spreadsheet application we recommend you use is the free NeoOffice suite, which is available at http://www.neooffice.org. Before you can view a generated report, you will need to install NeoOffice or another Open Document Format capable spreadsheet application on your computer.