Related articles:
Jul 04, 2016 How to customize the toolbar of your Mac’s Preview app. Like a number of Mac apps that come pre-installed with OS X, you can customize the toolbar in Preview to make way for buttons you’ll actually use and remove the ones you don’t. To do that, you’ll want to follow these steps. The menu bar at the top of your Mac's display acts as a convenient tray on which Apple serves you menus of your current app to the left along with more static status icons to the right.
Some windows on your Mac display a row of icons at the top of the window, known as a toolbar. While the toolbar gives you one-click access to commonly used commands, such as saving or printing a file, you may want to hide your Mac’s toolbar so that it doesn’t clutter up the appearance of a window.

To give you the option of hiding (or viewing) a window’s toolbar icons, a window might display a Toolbar button in its upper-right corner.
To toggle between hiding and displaying a toolbar, click the Toolbar button. Some programs may give you the option of hiding its toolbar another way, such as by choosing View→Hide Toolbar.
Remove Toolbar From Screen
Not all windows have a Toolbar button.