You can use Rufus to download Windows 10 ISO file - read how to do that in Work with the program section. Just rename the file rufus-3.8p.exe into rufus-3.8.exe and the program will work as regular, not portable application. The letter "p" in the file name means it will work as portable application, the program determines its mode by using this letter. You can use Portable Version, it needs no installation and it saves its settings into the program directory.
The old Version 2.18 works on Windows XP and Windows Vista, you can download old versions from downloads page: rufus.ie/downloads. It works on Windows 7 or later, 32 bit or 64 bit. Rufus is a Windows program that can create bootable USB drives for different operating systems like Windows and Linux. Rufus stands for The Reliable USB Formatting Utility.
How to use Rufus to create bootable USB on Windows 10 What is Rufus?