The Zoom To Selection button can be added to the Preview toolbar via the View menu's Customize... choice (available when a document is open in Preview). If you haven't added this button to your Preview toolbar, you won't need this article.
When you open a PDF document and press the Zoom To Selection toolbar button after using the Select Tool to define a specific portion of the page, the zoomed-in view will show the selected area as expected.
However, if you don't make a selection from the PDF before clicking the Zoom To Selection button, a blank page appears instead, and you will be unable to view or manipulate the document further until you close and open it again.
Close the document, and reopen it to view it again.
Remember to always select an area of the PDF document with the Select Tool (or just by holding your mouse button as you drag over an area of the PDF document) before clicking Zoom To Selection.
Or, remove the Zoom To Selection button that you previously added, and use the View menu's Zoom To Selection choice instead (this choice is dimmed when it cannot be used).
This document will be updated as more information becomes available.