There are several options for viewing the pages of a document. These options only affect how the document is presented on-screen. They do not affect final PDF output.
When Single Sheets is selected the document displays a single page per row. When Facing Sheets is selected the document displays two pages side-by-side. Facing Sheets can be useful for instance to view the two halves of a spread side by side.
Continuous Display is active the document displays
in continuous mode vertically. Vertical scrolling applies to the
entire document. When inactive only a single row of pages is shown at
a time. (One page if
Single Sheets is active, two pages if
Facing Sheets is active.) It is nonetheless possible to scroll
vertically through the document using the scroll-wheel on a mouse, or
using the [Page Up] and [Page Down] buttons on the keyboard.
When Book Mode is active, and Facing Sheets is selected, the view displays the first page by itself (like a book cover), and two pages side by side on subsequent rows. This is useful for controlling the order of the page spreads: odd pages left, or even pages left.
Sometimes a document’s pages are meant to be assembled seamlessly (for instance architectural plans printed across several sheets of paper). To preview pages in such a way turn off the display of Sheet Breaks.
PDF documents that define secondary display boxes (like crop and trim boxes) can be displayed with a preview of those boxes printed over each page. There are four types of boxes, and the display of each one can be turned on and off individually, or you can choose to turn the display of all boxes on or off with a single command.