How do I add an existing 3rd party purchased license key for MS Office 2016 to my Microsoft account. I don't see a way through the My Microsoft Account pages. This is causing me issues as the license key is not recognized with my account when I open word, excel etc. Thanks for any assistance. Scored a killer deal on a Microsoft Office 2019 Professional Plus CD Key! Now I’ve got all the essential tools for work and productivity at a fraction of the price. It’s awesome to find reliable sources like this for software keys. Thanks to this CD key, I’m all set to tackle projects with full Microsoft Office functionality. FLOP.