Splitting a long PDF into chapters usually means figuring out exactly which page each chapter starts and ends on, then splitting by page ranges manually. If the document already has a bookmarked outline, there’s a shortcut: the bookmarks already know where each chapter begins.
How it works
Split by Bookmarks reads the PDF’s existing top-level outline and uses it directly:
- Upload your PDF.
- It reads the existing top-level bookmarks (the table of contents entries).
- Preview the files it will create, one per bookmark.
- Download them individually, or all together as a ZIP.
Each output file is automatically named after its corresponding bookmark, so you don’t end up with a folder of generically numbered files you have to relabel by hand.
Pages before the first bookmark
Front matter — a title page, an introduction that comes before the first chapter’s bookmark — is included in the first split file, since there’s no earlier bookmark to start a separate section for it.
Nested bookmarks stay inside their parent chapter
A bookmark outline is usually a tree, not a flat list — open the sidebar in your PDF reader and you’ll often see section bookmarks indented underneath their chapter, one or two levels deep. This tool only reads the top level of that tree. A sub-heading bookmark nested under “Chapter 3” doesn’t get its own output file; its pages stay bundled inside whichever top-level bookmark it sits under, the same as if it weren’t bookmarked at all.
There’s no setting here to switch between “one file per chapter” and “one file per section” — it always works one level deep. If you need the finer split, you’ve got two workarounds: add flat, top-level bookmarks for exactly the sections you want with Create Bookmarks (anything you add there lands at the level this tool reads, regardless of what nested structure the original outline had), or skip bookmarks entirely and use Split PDF’s “Custom pages” mode with the section’s actual page numbers.
Two bookmarks landing on the same page
It’s common for a table of contents to have a bookmark for the section divider and a separate one for the first chapter that starts on that same page — or a “Contents” entry that happens to resolve to the same page as chapter one. When two bookmarks point at the same page, this tool doesn’t produce an empty file for the first one; it collapses them, and the earlier bookmark’s title becomes the name of the file that starts there. You end up with one file per distinct starting page, not one file per bookmark.
If your PDF has no bookmarks
You’ll see a message that none were found. That’s expected for documents that were never given an outline. If you already know which pages each chapter starts and ends on, Split PDF’s “Custom pages” mode gets you the same result directly — type each chapter’s range (e.g. “1-12, 13-30, 31-45”) and each downloads as its own file. Otherwise, it can still split by page count or target file size instead, or add bookmarks first with Create Bookmarks if you want the chapter-based split specifically.
Named destinations vs. direct page bookmarks
This tool resolves the common case of bookmarks that point directly at a page. Less common bookmark types — links to named destinations rather than a direct page reference — are skipped on a best-effort basis rather than causing an error.
Nothing here gets uploaded
The whole split runs in your browser tab, not on a server somewhere — so there’s no file-size cap or page-count ceiling imposed on you, and a thesis or scanned report doesn’t have to leave your device just to get broken into chapters. The only real ceiling is your own device’s memory, the same as any other job that reads a whole file in at once.