Copy/Paste creates a hidden files
These are AppleDouble files. As you discovered by opening them, they contain metadata for the files that you copied.

Since the disk is formatted as MS-DOS, OS X needs somewhere to store certain metadata for the file. This metadata is stored in an AppleDouble file. Such metadata includes Finder information and extended attributes.

These files begin with a dot, so are hidden. You shouldn't unhide these files, or modify them. You can remove AppleDouble files using dot_clean -m