How to add PDF bookmarks: a table of contents for long documents
Add outline bookmarks to a PDF entirely in the browser: no garbled titles, one bookmark per page, batch mode for many files, and nothing is uploaded.
A few hundred pages of textbook, contract or audit report, with no bookmarks, is like a dictionary with no index — you can only turn pages one by one. Smallpdf can do it, but it uploads; Adobe needs a subscription. What I wanted was local, free, and titles that do not turn into boxes.
Managing PDF bookmarks with TwoThink
Open PDF Bookmarks:
- Drop in the PDF; existing bookmarks are read automatically (if there are any)
- Add a title, pick the physical page number, and optionally a parent for nested levels
- "Bookmark every page" generates "Page 1" … "Page N" in one click
- After exporting, clicking a bookmark jumps to the right place in Adobe, in a browser or in Preview
Everything is processed locally in the browser: no uploads, no sign-up.
Will the titles come out garbled?
The PDF specification requires the outline Title to be UTF-16BE. We write it with a BOM, so mainstream readers display titles such as "Chapter 1" or "Appendix A" correctly in any language.
One bookmark for each of several PDFs
The "batch by filename" mode takes several PDFs at once and adds one top-level bookmark to each: the title is the file name without the .pdf extension, and it jumps to page 1. It is a quick way to tag every document in an archive folder, and the results download as a ZIP.
How it fits with merging and splitting
- Merge the files first, then add chapter bookmarks in one go
- Bookmark a long document before splitting it, so each part keeps its own outline (depending on the reader)
- An encrypted PDF has to be unlocked before its bookmarks can be edited
Summary
A long PDF without bookmarks is a waste of life. Add the table of contents locally, export, share — the shorter the chain of custody, the better. That is exactly why this tool exists.