You can open random files with it. From the command line, type `idea <filepath>`. If you already have a project open, the file will open in the same window as that project, but it isn't tracked as part of the project. If you don't have IntelliJ open yet, it starts a new instance with just that file.

That being said, even though I'm more comfortable with Jetbrains' editors, I still tend to edit miscellaneous docs in atom or vim.