How to Merge PDF Files Without Uploading Them
Most online PDF mergers upload your documents to their servers. For contracts, bank statements and ID scans there are better options.
Merging PDFs is one of the most common office jobs: a contract and its annexes, scanned pages that came out as separate files, receipts for an expense claim, the chapters of a thesis. Search for a PDF merger and the first results are websites that ask you to upload the files, process them on their servers and let you download the result. That is convenient, but the documents people merge are often exactly the ones they should keep to themselves.
Why uploading matters
When a file is uploaded, a copy exists on someone else's computer, at least for a while. Reputable services delete files after an hour or a day, but you have to take their word for it, and the copy still passes through their systems and logs. Some workplaces forbid uploading customer data or internal documents to outside services altogether, and data protection rules such as the GDPR make the company, not the website, responsible if personal data ends up there.
The alternative is to merge on your own device. There are three ways to do that: a browser tool that does the work locally, a program your computer already has, or a desktop application.
Option 1: merge in the browser without uploading
A browser can read and write PDF files itself. The PDF Tools on this site use pdf.js, the PDF engine Firefox uses to display PDFs, to draw page previews, and pdf-lib to write the new file. Both run as JavaScript on your device, so the documents are never sent anywhere.
- Open merge PDF and drop the files on the box, or click it to choose them.
- Put the files in order with the up and down arrows. Numbering the files beforehand, such as 01-contract.pdf and 02-annex.pdf, saves this step.
- To remove a blank scan page or turn a sideways one, open Organize pages first: every page appears as a thumbnail you can drag, rotate or delete.
- Press Merge and download.
You can check that nothing is uploaded yourself: open the browser's developer tools with F12, switch to the Network tab and merge. You will see the page load its two PDF libraries, and no request that carries your files.
Option 2: Preview on a Mac
macOS can merge PDFs without any extra software. Open the first PDF in Preview, show the thumbnails with View › Thumbnails, then drag the other PDF files from Finder into the thumbnail sidebar, at the place where they should go. Save the result with File › Export as PDF so the original stays untouched.
Option 3: Windows and desktop programs
Windows has no built-in way to combine PDFs; printing to Microsoft Print to PDF creates one file per document. The browser method above works in Edge and Chrome without installing anything. If you merge PDFs every day, a desktop program such as the free PDFsam Basic or a paid PDF editor does the same job offline and adds batch features.
On a phone, the browser method works too, although large scans are handled more comfortably on a computer, since every page is held in memory while you work.
What merging changes, and what it does not
| Part of the PDF | After merging with PDF Tools |
|---|---|
| Text, fonts and images | Copied unchanged; text stays selectable and nothing is re-compressed |
| Page size and orientation | Each page keeps its own; A4 and Letter pages can be mixed |
| Web links on the pages | Kept |
| Bookmarks (the outline in the sidebar) | Not carried over |
| Fillable form fields | Not carried over as interactive fields |
| Digital signatures | No longer valid in the new file, as with any change to a signed PDF |
The signature point deserves attention: a digital signature protects the exact bytes of the signed file. Any tool that combines a signed PDF with others produces a new, unsigned document. If the signature matters, send the signed file on its own next to the merged one.
Password-protected PDFs
A PDF locked with a password, or with restrictions against editing, cannot be merged by the browser tool; it says so instead of producing a broken file. If the document is yours, open it in the program that created it, remove the protection, and merge the unlocked copy. Working around a protection you did not set is not something a tool should do silently.
Keeping the merged file small
- Delete blank pages from scans before merging; a scanned blank page still weighs as much as a written one.
- If one of the files is a set of photos, turn it into a PDF with image to PDF after compressing the photos, rather than merging huge camera images.
- Merging never makes the pages larger: they are copied, not redrawn, so the result is roughly the sum of the input files.
Related jobs
The same tool splits a long PDF into parts with split PDF, keeps selected pages with extract PDF pages, and turns sideways scans with rotate PDF. To turn pages into images for a presentation or a chat, use PDF to JPG.