How to merge PDF files
- Drop your PDFs on the page or click Choose files.
- Drag the list (or use ↑ ↓) to set the order.
- Click Merge PDF, then Download.
Where does the merging happen?
Your PDFs are never sent anywhere. They are read into your device’s memory, and the open-source pdf-lib library copies every page, with its fonts and images, into a brand-new document. Nothing is re-rendered or re-compressed, so text stays selectable and images keep their original quality.
Because the work happens locally, the speed depends on your device, not your connection. Once the page has loaded, it even works in airplane mode.
What we measured
We merged 5 test PDFs of 10 pages each (50 pages, 5.6 MB in total, every page with text and a photo) in Chrome on a 4-core test computer. Merging took 0.06 seconds and the result was 5.6 MB, almost exactly the sum of the inputs, because pages are copied rather than re-encoded.
That last point matters: merging doesn’t make files smaller. If the combined file is too large to email, shrink the photos before you build the PDF with Compress Image and Image to PDF.
When it comes in handy
The most common job is sending a job application as one file: cover letter, CV, certificates and portfolio, in the order the recruiter asked for. Others bundle a month of scanned receipts for an expense report, put signed contract pages back together, or turn chapter-by-chapter lecture notes into a single handout.
Turn on Add a bookmark for each file and the merged PDF opens with a clickable outline, one entry per original file, which makes a 60-page bundle much easier to review.
Before you merge
- Password-protected PDFs can’t be opened. Remove the password in the app that created it first.
- A digital signature stops being valid once the document is changed. Keep the signed original and send it separately if the signature matters.
- Form fields that share the same name may end up linked, so typing in one fills the other.
- To use only some pages of a file, pull them out first with Split PDF, or reorder and delete pages afterwards with Organize PDF Pages.
Frequently asked questions
Are my files uploaded?
No. Everything happens inside your browser and deskumo never receives or stores your files. Close the tab and they’re gone from memory too.
Is there a limit on the number of files or their size?
There’s no fixed limit. The work uses your device’s memory, so on a phone it can slow down once the files add up to a few hundred megabytes. On a computer, much larger jobs are fine.
Will the quality drop?
No. Pages are copied as they are, so text, vector drawings and images are not re-compressed.
Does it work on a phone?
Yes. On iPhone (Safari) and Android (Chrome) you can pick PDFs from the Files app or your downloads, reorder them with the arrow buttons and save the result.
Can I merge only certain pages?
Merging works with whole files. Extract the pages you need with Split PDF first, or merge everything and remove pages with Organize PDF Pages.