When opening Microsoft Office documents from within TRIRIGA, Windows prompts for credentials. This does not happen for other documents such as PDFs. Windows credentials are being asked for as soon as you click to open a Microsoft Office document.
This is a third party issue reported by Microsoft. This happens in a local machine accessing TRIRIGA that has Microsoft Office 2003 or later installed. Go to the TRIRIGA Document Manager or a record and click on an Office document. On your machine, you have Office 2003 or later to read that document. In most intranet instances, this issue is most easily addressed by configuring the server to use Integrated Windows Authentication (IWA), and then configuring the client to enable automatic logon. The full resolution is described by the Microsoft document linked here: Authentication requests when you open Office documents (KB2019105).