Our PDF to Flipbook convertor can handle any size of document but all of the pages in the PDF must be the same height.
Single Page Layout
All of the pages in the PDF are the same width. This is the recommended layout

Double Page Spreads
The first page of the PDF is a single page and one or more of the internal pages are double page spreads.

If the PDF does contain double page spreads each one will be counted as 2 individual pages, the above example therefore has 6 pages.
While our PDF to Flipbook convertor has no problem with double page spreads they are incompatible with our Flipdocs Link Editor which is why we recommend separate pages.