How each split mode decides
By size weighs every page on its own (its content plus the images and fonts it uses), packs pages in order into parts below your limit, then writes each part and measures it for real. A part that still comes out over is split again, so the sizes you see are the files you get.
Ranges accept the usual notation: “1-3, 5, 8-” makes three files. Every N pages makes equal parts with a shorter last one. Bookmarks splits at the top-level bookmarks the document already has, and names each file after its bookmark.
A single page larger than the limit cannot be split further; the result marks it so you can compress that part.
Steps
- Add the PDF.
- Pick a mode: by size, ranges, every N pages or bookmarks.
- Check the parts listed with their page spans.
- Download one PDF, or a ZIP when there are several parts.
Limits, stated plainly
- Splitting copies pages with their resources, so fonts shared by many pages are repeated in each part; the parts can add up to more than the original.
- Bookmark mode needs a PDF with bookmarks (an outline).
Already have Preview or Edge? In Chrome or Edge you can open a PDF, choose Print → Save as PDF and type a page range to save part of a file. That works for one range at a time.
Engine: pdf-lib in a Web Worker; pdf.js reads the bookmarks. Your file is not uploaded; check it yourself.