When you search for "merge PDF online", almost every result works the same way: you upload your files to a server, the server combines them, and you download the result. That's fine for a flyer — and a real problem for contracts, medical records, payslips or anything with personal data in it.
The upload problem
Once a file leaves your device you're trusting someone else's infrastructure, retention policy and security practices. Many free PDF sites are monetized precisely because they see your documents. Even the honest ones keep files temporarily on servers you know nothing about, in jurisdictions you didn't choose.
Browser-based merging: how it works
Modern browsers can do the whole job locally. Libraries like pdf-lib read the raw bytes of each PDF in JavaScript, on your machine, copy the pages into a new document and hand you the result as a download. No network request ever carries your file — you can watch the network tab while it happens: nothing leaves.
That's exactly how the TurboTweaks PDF merger works:
- Drop your PDF files into the box (or click to browse).
- Reorder them with the arrows — the merge follows the list order.
- Click Merge and save the combined file.
Because there's no upload and no processing queue, it's also faster than server-based tools: a 50-page merge takes well under a second on a laptop.
Splitting and converting, same story
The same local-first approach applies to the rest of the PDF toolkit:
- Split a PDF — extract a page range into its own file.
- Convert images to PDF — each photo becomes a page.
- Turn PDF pages into images — rendered locally with pdf.js.
When a server is the right tool
Browser-side processing has limits: gigantic files are constrained by device memory, and jobs like OCR need heavyweight engines. For everyday merging, splitting and converting, though, there's simply no reason your documents should travel. Keep them on your device.