Full screen and zoom to page width in Preview or Skim on Mac

I got it now. I can right-click on the page, then select Single Page Continuous. With this setting, choosing Zoom to Fit Window will zoom to the page width.

Though this unfortunately isn’t available in full-screen view, you can choose View > Automatically Resize in non-full-screen view. Then click the green “+” button to make the window fill up the screen.

This issue baffled me for quite a long time too. All I wanted to do was view PDFs full screen as in "absolutely full screen" and be able to scroll between pages.

The trick here is to right click and select "Single Page Continuous".

Yes, it will go back to Single Page again, but now you'll have your PDF full screen. To scroll between pages, use the three-finger touch, not the two-finger one.