From the following links you can download each version of Office 2016 in English and Greek. Downloads are made from the official Microsoft download server: officecdn.microsoft.com.
The files are in the form of IMG images and not ISO. These are files that you can burn to CD, DVD or USB. They need the product key to install.
The IMG images are not the same as the ISOs available in Digital River, but also the "Click-to-Run" versions of the instant installation.
If you need another language let us know in the comments of the post to add it.
Download the images that interest you