Create .DMG file on Windows 10 PC

I need to create a bootable flashdrive to boot an iMac 21,5 inch (model late 2009) for installing OSX (the internal DVD-drive and harddrive are failing). I do have an official DVD from Apple with OSX Snow Leopard. I asked Apple support how to proceed. They send me the following procedure:

http://pureinfotech.com/make-bootable-usb-mac-os-x-windows/

Question: how do I create the .DMG file on a windows PC using the official DVD from Apple? My other computer is a modern Windows 10 Pro PC. Please advice.