How to split a PDF by chapter or for email
Open Split PDF. For chapters, choose One file per bookmark. To fit a size limit, choose By file size and type the limit, such as 10 MB. Then press Start and download the parts.
Splitting by chapter
One file per bookmark starts a new file at each top-level bookmark and names it after the chapter. Pages before the first bookmark, such as a cover, get their own file. If the PDF has no bookmarks, look up where each chapter starts and type ranges such as 1-14, 15-32, 33-.
Getting under an attachment limit
Choose By file size and type the limit your email or the portal gives you. Each part holds as many pages in a row as fit, and its size is checked by saving it. If one page is bigger than the limit on its own, compress the PDF first. The receiver can put the parts back together with Merge PDF.