my files turned into an exec files

why my files that are in my flash disk turned into an exec files? there's also .ink behind it. one of my friends, copied one of my files and her laptop is not a mac while in the school. and when I got home, i was going to check some files that one of my teacher gave me yesterday (this is the one that my friends copied too) and it turned out to be an exec files. and i can't barely open it. my flash disk is also new, and my first files is the one that the teacher gave me. I wonder what is happened. Can anyone help me? Thanks