Mineforge not working :/

I'm not sure if this is the right place for this but I hope it is.

So I wanted to try some mods and I saw most of them used Mineforge to work, I downloaded Mineforge but when I tried to run it, it was a image file, and my picture displayer (Windows Photo Viewer) said "Windows Photo Viewer can't open this picture because either Photo Viewer doesn't support the file format, or you don't have the latest updates to Photo Viewer" Now, I do have the latest updates for my viewer.
Soooooo.... What do I do?

P.S. I'm using Windows 8.1 if that helps