Why this runs entirely in your browser
A PDF you’re merging is often something you wouldn’t want sitting on someone else’s server even briefly: a signed contract, a tax form, a scan of an ID. Most online merge tools upload your files to process them, which means trusting a third party with whatever’s inside. This one doesn’t: the actual merging happens using a PDF library that runs directly in the browser, so your files never leave your device in the first place.
How merging actually works
A PDF file is really a container of pages, each one a self-contained object with its own content, fonts and images. Merging doesn’t flatten anything into a picture or re-typeset the text: it copies each page object from the source files directly into a new container, in the order you choose. That’s why the result is lossless: what comes out is pixel-for-pixel and byte-for-byte the same content you put in, just repackaged into one file.
Ordering matters, and it’s yours to set
The files combine in exactly the order they appear in the list (top to bottom), with each file’s own internal page order left untouched. If you’re combining a cover page, a report, and an appendix, add them in any order and then drag them into place, or sort the list by name; there’s no need to add anything again to fix the order. Each file shows previews of its first pages, so you can check you have the right ones.
What this tool doesn’t do
Merging only combines whole files: it doesn’t compress file size, edit content, or read text out of scanned images. To move or delete single pages, merge first and then use Organize PDF on the result; to pull specific pages out of a document, use Split PDF.