There are several options for viewing PDFs/book-like items in Digital Collections:
[1] Toggle Thumbnails: See all the pages of the book at the bottom of the viewer as a "film strip".
[2] Page Buttons: Icon functions from left to right: First Page, Flip Left, Enter a Page Number, Flip Right, Last Page.
[3] Zoom function
[4] Search Text Function
[5] View Mode: Choose between: one-page view, double-page view, four-page view
[6] Toggle Fullscreen Mode
On smaller displays or minimized windows the function buttons may be hidden.
For best results orient your device to landscape, maximize your window, or refresh your page/select Actions>Open to reset the viewer popup to use the fully display available.