We have a post that shows you how to legally download all Windows ISO media files but here is a tool called Microsoft Windows and Office ISO Download Tool that offers a much better way.
It’s a free 3rd party portable tool that lets you find and download genuine Windows and Office ISO media files, including Windows 7, 8.1, 10, 10 Insider Preview, Office 2007, 2010, 2011, 2013, and 2016. Even though it’s not an official tool provided by Microsoft it does download genuine ISO files for both Windows and Office, which are only good for people who already have purchased licenses to use these programs.
Head over to the download page and download the tool there. Then simply click the executable file to launch the tool. It does require .Net Framework 4.6.1 and IE 11 to run but if you only have .Net Framework 3.5 installed, you can use the legacy version instead.
Select the product you want to download from the Choose Software section on the right, then pick the right edition or language from the Select Edition drop-down list, and click Confirm button to start the process. The list of edition could be quite long in certain products. For example, in Windows 10 Insider Previewer category, you can download editions all the way back to 14262 while the current one in faster ring is 14931.
All download links provided in the tool point back to the genuine ISOs on the Microsoft site. There are no files hosted elsewhere on the internet. So it’s safe to click and download them. I’ve also checked the tool on VirusTotal which came out clean.