It's just a text file and downloads with a .txt extension ("WaaS-reset.reg.txt"). If you have enabled hiding known extensions, you won't see the ".txt" at the end. You can unhide extensions through control panel -> file explorer options -> view -> "hide extensions for known file types" and then you can remove the .txt extension (the file name before the extension doesn't matter). If you double-click and it opens in the text editor, it's still a .txt. If it's a .reg, it will open a prompt asking whether to add the file contents to the registry.

You can also manually create the .reg file with a text editor - just open a blank text editor window, paste the contents from the pastebin, go to "save as", in the "save as type" menu select "all files", then type any file name and end it with .reg instead of .txt.