How to rip ISO instead of MDX, or how to convert MDX to ISO?

I need to create a bootable thumb drive version of Win7, so I downloaded Daemon Tools Lite and made the disk image, but the problem is that the image is in an MDX format instead of ISO.

I don't know why Daemon Tools would do that, but I need to have an ISO file on my computer in order for the Windows 7 USB/DVD Download Tool to work.

What should I do?