Beat email attachment limits by compressing before splitting, break long documents into per-chapter files named after their bookmarks, and add an outline when your PDF has none.
There are two reasons to break up a PDF: something imposes a size limit, or the document is long enough that people need to navigate it. Those need different tools — and if your document has no bookmarks, the second problem has a prerequisite most people miss.
Email attachment caps and upload forms that reject anything over 10 MB are the usual culprits. Split by Size fills each part up to your limit and starts a new one before exceeding it.
It is best-effort rather than exact, because pages cannot be broken mid-page — parts come in under your target rather than precisely on it. A single very heavy page can still exceed a small limit on its own, in which case compress the document first.
Which raises a better question: should you split at all? Running the file through the PDF Compressor often gets you under the limit in one step, and one file is easier for the recipient than five. Try compressing before splitting.
For a long report or book, splitting by arbitrary page ranges produces fragments nobody can identify. Split by Chapters uses the document's own bookmarks, so each top-level entry becomes its own file.
The practical advantage is the naming. Output files are named after the bookmark titles, so you get 03 - Methodology.pdf rather than part-3.pdf — immediately identifiable without opening anything.
Splitting by chapters requires bookmarks, and plenty of PDFs have none. Documents exported from Word with proper heading styles get them automatically; scans and simple exports do not.
That is what Edit Table of Contents is for. It adds or edits the outline — the clickable navigation shown in your reader's sidebar — which is worth doing for its own sake on any long document.
Worth being clear about the distinction: a contents page is printed content, text on page two listing where things are. Bookmarks are navigation built into the file, letting a reader jump to any section from anywhere. Long documents benefit from both, and they are entirely independent.
Aim for enough bookmarks to reach any major section in one click without turning the sidebar into a wall of text. Chapter or section level is usually right; every heading in the document is more than most readers want.
| Situation | Do this |
|---|---|
| File is too big to email | Try compressing first, then split by size |
| Long document, want one file per chapter | Split by chapters |
| Document has no bookmarks | Add an outline first |
Each part is a complete, independent PDF that opens normally, with text still selectable and images at their original resolution. What does not survive is anything document-level that crossed the boundary — a bookmark pointing at page 40 is meaningless in a five-page part, and internal cross-references lose their targets. That is inherent to becoming separate files.
Compress before you split when size is the issue. Split by chapters when structure is, and add bookmarks first if the document lacks them — that outline is useful on its own, and it is what makes chapter splitting produce sensibly named files instead of anonymous fragments.