If you want an .ISO file, select the ‘ISO file’ option. You can use the .ISO file to create either an installation DVD or USB Flash drive.
By default the name of the .ISO file (No matter what Language, Edition and architecture you choose) will be “Windows.iso”. If you plan to download more than 1 version, rename the Windows.iso file before you start the next download.
The file that is actually downloaded is not in .ISO format but an intermediate / temporary file that is used to create the .ISO file.
When the download has complete the intermediate / temporary file is verified / checked for file corruption which may have taken place during the download or was corrupted due to a bad spot / sector on your disk drive.