The two bytes that start the file on line 1, PK are a dead giveaway that this is a zipped archive file, as Peter indicated. Long ago, zip files were created with a program called pkzip.exe and their contents extracted with a program called pkunzip.exe. I think P was for the name of someone named “Phil”. I’ll really press my memory and say the K was for “Katz”. (I could cheat and google it, but it is often more fun to just try to pull stuff from memory – googling it is left as an exercise for interested readers)