How to merge PDF files
- Drop your PDF files onto the box above, or press Choose files. Each file appears as a card with a thumbnail of its first page, its size and its page count.
- Put the files in the order you want. Drag the cards, or use the ↑ and ↓ buttons — they also work from the keyboard.
- To use only part of a file, type the pages into its Pages box:
1-3, 5takes pages 1, 2, 3 and 5;4-takes page 4 to the end;3-1takes pages 3, 2 and 1 in that order. Leave it empty to include every page. - Press Merge PDFs. The combined file downloads as merged.pdf, and a summary shows how many pages it has and how large it is.
If a file cannot be used — it is encrypted, damaged or not really a PDF — its card turns red with an explanation, and the merge button stays disabled until you remove it.
What happens to your files
A PDF file is a collection of numbered objects — pages, fonts, images, annotations — plus a cross-reference table that says where each object starts. Each page is an object that points to its content stream, the resources it uses and its size. Merging does not need to redraw anything: it copies the selected page objects, together with every font and image they depend on, into a new document and writes a new cross-reference table.
This page does that with pdf-lib, an open-source PDF library, running in a background thread of your browser. Because pages are copied rather than re-rendered:
- text stays selectable and searchable, and vector graphics stay sharp at any zoom;
- images are not re-compressed, so there is no quality loss;
- each page keeps its own size and orientation — you can merge A4 portrait pages with Letter or landscape pages and each one stays as it was;
- a page that was already rotated with the PDF /Rotate setting keeps that rotation.
Thumbnails and page counts are produced with pdf.js, the PDF renderer used in Firefox. Both libraries are loaded from this site, and the file bytes stay in the page's memory the whole time. You can check this by watching the Network tab of your browser's developer tools while you merge.
What is not carried over
Document-level features belong to the original file rather than to its pages, so they do not survive a page-level merge: bookmarks (the outline), form field definitions that span the document, embedded file attachments, document-level JavaScript and digital signatures. A signed contract that is merged into another file is, correctly, no longer signed.
Examples
| Input | Pages setting | Result |
|---|---|---|
| a 3-page portrait report and a 2-page landscape table | both empty | 5 pages; pages 4 and 5 stay landscape |
| a 3-page file | 3, 1 | 2 pages: page 3 first, then page 1 |
| a 10-page file | 1-3, 5 | pages 1, 2, 3 and 5 |
| a 6-page file | 4- | pages 4, 5 and 6 |
| a 3-page file | 3-1 | pages 3, 2, 1 — reversed |
| a 10-page file | 11 | refused: the file has only 10 pages |
A typical use is an application pack: a cover letter from a word processor, a scanned signed form and two certificates, merged in that order into one file that a portal will accept. Another is dropping the blank reverse sides from a double-sided scan by listing only the odd pages, such as 1, 3, 5, 7.
Limits
- Password-protected files cannot be merged. A PDF with an open password is encrypted, and copying its pages without decrypting them would produce unreadable pages. Remove the password in a reader you trust (open with the password, then save or print to a new PDF) and add the copy. Files that are only restricted against editing are also encrypted and are refused for the same reason.
- Size is limited by your device's memory. Merging a few hundred megabytes works on a desktop; a phone may run out of memory with very large scans.
- The output is not compressed further. The merged file is roughly the size of the selected pages added together. Merging does not shrink scans.
- Bookmarks, signatures and attachments are dropped, as explained above.
- Damaged files. Some slightly damaged PDFs open in a reader but cannot be parsed reliably. Re-saving them from a reader usually fixes this.
Frequently asked questions
Are my PDFs uploaded to a server?
No. The files are read and combined inside your browser, and the merged file is created on your device. Nothing is sent over the network, which you can confirm in the browser's developer tools.
Is there a limit on the number of files or pages?
There is no fixed limit and no daily quota. The practical limit is your device's memory: dozens of files and thousands of pages are fine on a typical laptop.
Will the merged PDF have a watermark?
No. Pages are copied exactly as they are; nothing is added to them.
Can I merge only some pages of a file?
Yes. Type the pages into the Pages box on that file's card, for example 1-3, 5 or 4-. Leave the box empty to include every page.
Why is my file rejected as password-protected when it opens without a password?
It probably has an owner password that restricts editing or printing. Such files are still encrypted, and their pages cannot be copied without decrypting them first. Print or save the file to a new PDF and merge the copy.