No, really. Preview.
Yes, it can open everything (I don't know where I suggested that it is only for PDFs?)
But it doesn't act like other editors. There's no save dialogue when you, for instance, rotate a PDF.
The term 'Preview' in other programs, like when using a scanner or other text editors, is a non destructive type of viewer. Just a viewer. "preview before you make changes"
But preview on OSX changes that.