Merge PDF Files
Combine multiple PDFs into a single file, in whatever order you choose. Add your files, arrange them, and download the merged PDF. Nothing is uploaded, it all happens on your device.
Click to choose PDF files, or drag and drop them here
Add two or more PDFs. Stays on your device, nothing is uploaded.
Are my PDF files uploaded anywhere?
No. Merging happens entirely inside your browser using JavaScript. Your files never leave your device or touch a server.
Can I choose the order the PDFs are merged in?
Yes. Add your files, then use the up and down buttons on each row to arrange them in the order you want before merging.
Is there a limit on file size or number of PDFs?
There's no hard limit built into the tool. The practical ceiling is your browser's available memory, very large or numerous files may take longer or struggle on low-memory devices.
Does merging reduce PDF quality?
No. Pages are copied as-is from each source file, there's no re-rendering, re-compression, or quality loss.
Can I merge a password-protected PDF?
Not currently. Password-protected or encrypted PDFs can't be read by the tool and will show an error, remove the password first with a PDF reader.
How it works
The merge runs on pdf-lib, a PDF library that operates directly on the file's internal
object structure in your browser's memory. When you click merge, the tool creates a fresh
empty PDF, then walks through your files in the order listed and calls
copyPages() on each one. That copies every page object along with everything
the page references: its fonts, images, vector graphics, and annotations. Nothing is
rendered to pixels at any point, so a merged page is byte-for-byte the same drawing
instructions as the original. That's why merging never blurs text or recompresses images,
and why a 200-page merge finishes in seconds.
One honest caveat worth knowing: copyPages() copies the page tree, but a
PDF's bookmarks (the outline sidebar in your reader) and interactive form definitions
live in a separate part of the file called the document catalog, which isn't copied. So
if your source PDFs have bookmark outlines, the merged file won't show them, and filled
form fields can behave oddly. The visible page content always comes through intact.
Most online mergers do exactly the same thing, they just don't tell you.
A side effect of per-file copying: if two source PDFs embed the same font, the merged file carries two copies of it, so the output can be slightly larger than the sum of its parts. If size matters afterwards, run the result through the compress tool.
Your files never leave the tab. You can verify this yourself: open DevTools, switch to the Network tab, add your PDFs, and merge. No request carries your documents anywhere, because pdf-lib does all its work in local memory and the download is generated from a blob on your own machine.
From the blog: How to Merge PDFs for Free (No Software, No Sign-up)