I recently downloaded a textbook as a .djvu file (sighs, not a PDF. wth is this). I found a way to view it and a way to convert it on the Internet (cool).
Recently however, I downloaded Homebrew for my Mac, and I found a strange file that was called djvu2pdf.rb (this sounds like it does what I want it to do) inside of the folder ~/homebrew/Library/Formula.
Among the spotlight search for djvu I did were these files:

What is this file for? Does it have anything to do with converting a .djvu to a .pdf? If so, how do I use it?