PDF Merger
Merging PDFs is the most common reason people upload confidential documents to a random website. Contracts, medical records, tax returns, and signed agreements all routinely pass through free online mergers. This one runs in the page, so the files never leave your machine.
How to use it
- Drop in two or more .pdf files. They merge in the order you select them.
- Pages are copied into a new document using pdf-lib, in the browser.
- The combined PDF downloads immediately.
How the merge is performed
A new empty document is created, then every page of each source is copied into it in order. Copying a page brings its content stream along with the resources it references: embedded fonts, images, and colour profiles.
Because the copy is structural rather than a re-render, page content is not rasterized or recompressed. Text stays selectable and searchable, vector graphics stay vector, and quality is unchanged. The merged file is the same pages in a new container.
Why the merged file is smaller than the sum of its parts
PDFs embed their fonts, and a font subset can easily be several hundred kilobytes. When ten documents produced from the same template each embed the same font, merging deduplicates shared resources rather than storing ten copies.
The saving is largest exactly where you would expect: batches of invoices, reports, or statements generated from one system. Merging unrelated documents that share nothing produces a file close to the sum of the originals.
What is lost, and what blocks the merge entirely
Document-level features belong to the file rather than to individual pages, so they do not survive being copied page by page.
Specifically:
- Bookmarks and the outline tree are attached to the document, not to pages, so the merged file has no outline. For a long merged report this is a real loss and usually needs rebuilding.
- Interactive form fields lose their values, and fields sharing a name across documents collide. Flatten forms before merging if the entered data matters.
- Digital signatures are invalidated. This is by design: a signature attests to the exact bytes of the document it signed, and merging changes them. Any tool that claimed otherwise would be broken.
- Document-level JavaScript, attachments, and named destinations used by cross-document links.
- Password-protected files cannot be merged at all. Remove the protection in a viewer that has the password first.
At a glance
| Accepted input | .pdf, two or more files |
|---|---|
| Order | Selection order |
| Page content | Copied, not re-rendered |
| Encrypted files | Not supported |
Frequently asked questions
Are my documents uploaded anywhere?
No. Merging happens entirely in the page using a JavaScript PDF library. Nothing is transmitted, which is the main reason to use a client-side tool for confidential documents.
Can I control the page order?
Files merge in the order you select them. To interleave pages from different documents, split them first and merge the resulting pieces in the order you want.
Why does my encrypted PDF fail?
Encrypted documents cannot be read without the password, and the tool does not prompt for one. Open the file in a viewer, remove the protection, and save an unprotected copy.
What happens to my bookmarks?
They are lost. Bookmarks live at the document level rather than on pages, so copying pages into a new document leaves them behind. They need rebuilding in a full PDF editor.
Read more
Working with documents: PDF, DOCX, and spreadsheets — Document formats encode intent as much as content, and conversions between them succeed or fail on whether that intent was recorded.