The page count for your booklet must be a multiple of 4.
For example: 8 pages, 12 pages, 16 pages, 20 pages, 24 pages, 28 pages etc.
The maximum page count is 84.
If you page count is not a multiple of 4, blank pages will be automatically added to the back of the booklet.
For example: a 10 page file will have 2 pages to added. Making a total of 12 pages.
Pagination example for an 8 page booklet: