I need to open a RUF file

I have a thumb drive with a .RUF file on it. My iMac is running mac OS Sierra 10.12.1 I looked it up, and a RUF file is associated with a Blu-ray file, but I don't have a way of opening or playing it on the iMac to see what it is. Just from an internet search, a RUF file can be opened using Windows, but it was from a 2011 post. I can't find anything recent. A workaround suggested was to burn it to a CD and play it, but if it's a Blu-ray file, doesn't it have to be burned to a DVD? And I'm not sure this iMac has DVD burning capabilities.

Do I just have a really old file that is no longer accessible?

Thanks all you techie geniuses! Please use simple terms. I am a grandma.