In the past, it wasn’t easy for customers to get the installation files, but starting with Windows 8, things started to change as Microsoft slowly began relaxing the rules to let anyone download the files to make a clean install of Windows.
When it comes the time to reinstall Windows on your system, because things are not working correctly or simply because you want to do a clean installation, you’ll need the ISO containing the files to create a bootable media to install the operating system.