Once the download is complete, right click on the downloaded file and choose the “Mount” option from the dropdown menu.
After the ISO file that you downloaded is mounted, you can access it from your Computer as a DVD drive. Here you can run the installer.
Complete the program installation and enter the “activation key” during or at the end of the process.
Once the download and the installation of the program is complete, enter the activation key when running any application from the Microsoft Office package, for example Microsoft Word. It usually will be the first thing that you will be asked for. Should that dialog not pop up you can enter the registration key in the “File” menu under “Account” (Office 2013/2016/2019) or under “Help” (Office 2010).