I think those are linkages that MacOS uses to determine how to handle the files. They serve somewhat the same function as a file extension and registry entry in Windows—they tell the operating system what program to use to open a file when you double click on it. It's why sometimes you get Preview when you open a pdf and sometimes you get Acrobat—it depends on what's in that accessory file instead of what the extension is. When you're actually using a Mac, they're invisible, and if they're not present, the computer will build them as soon as the file is accessed.