One copy of Microsoft Office can suffice for multiple machines, saving you the cost and hassle of having to purchase redundant copies of the same software. Accomplishing this will require a "Volume Licensing Key," which is an official authorization allowing you to use the same piece of software on more than one computer at a time. While obtaining this key is not free, it is sure to be less expensive than purchasing a copy of Office for each machine.
Contact Microsoft or your computer manufacturer to obtain a Volume Licensing Key for your copy of Office. This key will consist of a product code that is designed to work on more than one machine at a time, allowing you to register multiple copies of Office concurrently without any trouble. The Volume Licensing website for Microsoft is www.Microsoft.com/licensing/about-licensing/how-volume-licensing-works.aspx.
Install a copy of Office on one computer at a time, using your single copy of Office to install the software on each machine. Input your Volume Licensing Product ID Key during the setup procedure to active each copy of Office.
Complete the software registration process either online (following the on-screen prompts during the installation process) or over the phone (by calling the hotline that appears during the installation process). Completing the registration using your valid Volume Licensing Key will prevent Office from automatically deactivating itself after the designated period, granting you full access to product updates for all of your computers.