Final answer:
To add roles and features to a down-level server such as Windows Server 2008 from a newer system, use the Remote Server Administration Tools (RSAT), which include the Windows Admin Center and the Add Roles and Features Wizard in Server Manager.
Step-by-step explanation:
The tool used to add roles and features to a down-level server, such as Windows Server 2008, when managing it from a newer version of Windows Server is the Remote Server Administration Tools (RSAT). RSAT allows administrators to manage the functionalities of older Windows Server versions from a remote computer running Windows 10 or a newer Windows Server version.
To install roles and features on a down-level server using RSAT, you would typically use the Windows Admin Center or the Add Roles and Features Wizard in the Server Manager on the newer Windows Server edition or enabled RSAT on Windows 10. It's important to ensure compatibility and proper network configuration for successful remote management with these tools.