Downloaded something that just ends in .file, how do I open it?

Usually that means the browser couldn't work out what the file was, so it gave it a generic name. The file itself is probably fine. Quick way to tell: open it in Notepad and look at the first few characters. %PDF means it's a PDF, PK means a zip (or a Word/Excel file, those are zips inside), and JFIF or Exif near the top is a photo. Rename it to .pdf / .zip / .jpg to match and it'll open. If it came from somewhere you don't trust, don't rename it to .exe and run it to find out.