Is it possible to use Preview to highlight text or a portion of an image from a screenshot (on macOS High Sierra)?

I am trying with both a PDF and/or a PNG file, but this does not seem possible. Nothing I am trying works. Is it possible to take a screenshot natively in macOS, then highlight a portion of said screenshot? If so, how can this be done exactly? To be clear, I want to just use native tools that are built-in to macOS, so **Preview** in this case.