So if you are using Windows 8.1 or older versions, you will not be able to install it. However, I regret to inform that according to the disclosures, Microsoft Office 2019 only works on Windows 10. It is stable one, this means you can download and use it right now without worrying about fatal errors which you have gotten in beta versions before. After a series of preview versions, Microsoft finally came out with an official version of Office 2019.
