You can Collaborate for free with online versions of Microsoft Word, PowerPoint, Excel, and OneNote. Save documents, spreadsheets, and presentations online, in OneDrive. Microsoft Office setup require valid office product key which needs to be redeem at office.com/setup. After redemption you can download install or reinstall office apps on your computer device. Office Product key is one time license to download , install ,reinstall of renew office 365 subscription.