A new feature in macOS Mojave is the ability to edit and manipulate files directly in the Finder using Quick Actions. You can rotate and mark up images, mark up PDFs, trim video and audio, and even convert images to PDF files. In the future you will be able to do more with third-party extensions. You can currently build your own Quick Actions in Automator too.
Yeh... Quick Actions...
So how do I *HIDE* this feature and keep my preview pane?
Mark: Just don't use the feature. If you don't use them, they are just buttons.