nothing leaves your device
Merging a PDF should not require uploading it
Most PDF merge sites work the same way: you hand over your file, a server does the work, and you trust a privacy policy about when the copy gets deleted. For a contract, an invoice batch or a set of medical scans, that is a strange trade to make for an operation that is mostly just copying page objects from one file into another.
This tool does the copying in the browser tab you already have open. Your files are read with the File API, assembled with pdf-lib in memory, and handed back to you as a download. There is no upload step to opt out of, and the page keeps working after you go offline.
three steps
How to merge PDF files
Add the files
Drop in up to 20 PDFs — each one is checked and its page count shown.
Set the order
Move files up or down; the list is the order of the finished document.
Download
One PDF with every page, in that order.