How to merge PDF files without uploading them

Most "merge PDF" websites work by uploading your files to their server, combining them there and sending the result back. For a recipe that's fine. For a signed contract, a payslip or a scanned passport, it means trusting a stranger's server with a copy. You can avoid that entirely: modern browsers are capable of editing PDFs themselves.

Merge in the browser, step by step

1. Open the Merge PDF tool.
2. Drop your PDF files onto the drop zone, or click it to choose them. You can add files in several goes.
3. Put them in order with the ↑ and ↓ buttons. The merged document follows the list from top to bottom.
4. Click Merge & download. The combined PDF is created on your device and saved like any other download.

The first time you use a PDF tool your browser downloads pdf-lib, an open-source PDF library, from the cdnjs CDN. That request contains the library, not your documents. After that, all of the work happens in the browser tab's memory.

Check for yourself that nothing is uploaded

You don't have to take a website's word for it. In Chrome, Edge or Firefox:

1. Open the tool, then press F12 (or Cmd+Option+I on a Mac) and choose the Network tab.
2. Tick Preserve log, then merge your files as usual.
3. Look at the Method column. An upload would appear as a POST or PUT request whose size is roughly the size of your files. On this site you will see only GET requests — the page, its scripts, and the library.

For extra certainty, load the tool, then switch off Wi-Fi before merging. Once the library has been fetched, the merge still works offline.

What gets carried over — and what doesn't

• Pages, text, images and vector graphics are copied exactly; nothing is re-compressed.
• Bookmarks (the outline panel) belong to each source document as a whole, so they are not carried into the merged file.
• Interactive form fields may lose interactivity when copied between documents. Fill and flatten forms before merging if the filled-in values matter.
• Password-protected PDFs can't be merged until the password is removed in the program that set it.
• Size is limited by your computer's memory rather than an upload quota. Hundreds of pages are usually fine on a laptop; phones have less room.

Other offline options

If you'd rather not use a website at all: on a Mac, open the first PDF in Preview, show thumbnails, and drag the other PDFs into the sidebar. On any system with the free command-line tool qpdf:

qpdf --empty --pages first.pdf second.pdf -- merged.pdf