How merging works here
Most PDF sites upload your file to a server, merge it there, and hand back a download link. This one does not. When you drop files in, the browser reads them into memory, a Web Worker stitches the pages together with pdf-lib, and the result is handed straight back to you. No request carrying your document is ever sent — which you can verify in your browser's network tab.
Limits
Up to 20 PDFs at once, 100MB per file, and 200MB across the batch. These are memory limits, not business ones — there is no account, no queue, and no paid tier that lifts them. If a very large merge fails, a desktop browser has more headroom than a phone.
Does merging change my pages?
No. Pages are copied across intact, so text stays selectable and searchable and image quality is untouched. If you need a smaller file afterwards, run the result through Compress PDF.