To upload a book extract with discontinuous pages you can use commas to enter the required page numbers. For example “5-10,20-25” is a valid input if your file contains pages 5 to 10 and 20 to 25. If you want to include the book’s cover page and content page, you can enter “COVER,30-40" for example.
Please make sure the total number of pages in the file you upload matches the number of pages you enter. If there is a publisher original file available, you can use the same method to extract discontinuous pages. For example “80-90,100-110” will only select those pages out of a file that contains all pages of a book.
If you require assistance in organising pages within a pdf, you can follow the steps in this article: https://helpx.adobe.com/au/acrobat/using/manipulating-deleting-renumbering-pdf-pages.html