Side-by-Side view:
The viewing area is split into three sections. The most recent revision of the selected file appears in the left section, and the next most recent revision appears in the middle section.
Smart Review compares the two files, generates a comparison image, and displays it in the right section.
Stacked view:
The viewing area is split into three sections. The top and middle sections contain the images to compare, and the bottom section contains the comparison image.
If the file that you opened is a page in a multipage file, the first page of the file automatically appears in the top section and the next page of the file (from the Files pane) automatically appears in the middle section.
The comparison image in the right or bottom section is automatically refreshed to display any differences between the two selected revisions.