How to use the merge pdf with bookmarks
- Choose two or more PDFs. Each file is shown with its pages and size.
- Set the order with Up and Down, and edit the bookmark title of each file. The title starts as the file name without .pdf.
- Tick Keep each file's own bookmarks as sub-bookmarks to rebuild the bookmarks each file had, nested under its title.
- Choose Merge and download.
How the bookmarks are built
A PDF bookmark, also called the outline, is a tree of titles that each open a page. This tool copies the pages of every file into one document in the order shown and writes one top-level bookmark per file that opens its first page. If you keep the original bookmarks, the tool reads each file with pdf.js, finds the page each bookmark points to, and rebuilds them under the file's title with their new page numbers. A bookmark that points nowhere, or past the end of its file, is left out. In a test with files of 2, 3 and 1 pages, the second file having a chapter on its page 2 and a section on its page 3, the merged file has 6 pages and bookmarks at pages 1, 3 and 6, with Chapter on page 4 and Section on page 5.
Each file is read with pdf-lib and its pages are copied into the new document. Bookmarks that were in the originals are not copied by the merge itself, which is why the rebuilding step exists. Links inside the pages and form fields are kept only where the PDF library can copy them, so check a merged form before you rely on it.
Limits and related tools
Up to 100 files of 25 MB and 1,000 pages in total can be merged. Password-protected PDFs are refused, because the tool does not try to open them. For a simple merge without bookmarks use merge PDF; to check the outline of a result, the PDF outline viewer; to change the page numbers a viewer shows, the PDF page labels editor; and to cut a file into parts, split PDF.
The files are joined in your browser and nothing is uploaded.
Assumptions and limits
- Each file is a normal, unencrypted PDF of up to 500 pages.
- Bookmark titles are taken as typed, up to 120 characters. Control characters are not allowed.
- Destinations open the page in a fit-page view. The original zoom of a bookmark is not kept.
- The merged file is saved with new internal numbering, so file size can differ from the sum of the parts.
Frequently asked questions
Will my original bookmarks be lost?
Not if you tick the sub-bookmark option. The tool reads each file's bookmarks and rebuilds them under the title for that file. Without the option, only one bookmark per file is made.
Can I rename a bookmark?
Yes. Each file has a title box. Edit it before you merge. The first top-level bookmark opens the first page of that file.
Why does a bookmark open the wrong page?
The page number in the original may point to a page that was removed or a named destination that could not be found. Those bookmarks are left out instead of pointing to a wrong page.
Does the order I choose change page order?
Yes. Pages appear in the order of the files in the list, each file's pages in their own order. Move a file with Up or Down before you merge.