If you want to have windows .iso files for various purpose like you want to have windows 7 in virtualbox, then you need an .iso file. There are many methods of creating an .iso from installed windows. But what if microsoft provided all of them( I mean 7,8 &10) free of cost. The only requirement is that you own a product key for the respective Windows edition (and that's also is not a painful task to get).
https://www.microsoft.com/en-us/software-download/techbench here, Microsoft has only provided the Windows 10 editions.
now In your browser tab (which is in Step-1) press ctrl+shift+j (chrome & firefox) and paste the copied data and press enter.
wow! now you can download any windows version.
(Note that: the download link only exist for 24hrs from the time of creation.)