Never "buy" an ISO file from a third-party site. These can be tampered with or contain malware. Always get the official file directly from Microsoft using their Media Creation Tool or direct ISO download pages.
Go to the Windows 10 Download Page and use the "Create Windows 10 installation media" tool. Choose the ISO file option during the setup process. 2. Buying the License (The "Activation") buy windows iso
To use Windows legally and remove "Activate Windows" watermarks, you need a license. You have a few legitimate paths: Never "buy" an ISO file from a third-party site