Why merge PDF files?
PDFs often arrive as separate pieces — a signed cover page, a scanned ID, individual invoice pages, chapters of a report — but most workflows expect one document. Email attachments, application portals, and print shops are far easier to work with when everything is a single file with the pages in the right order, instead of a folder of loose PDFs the recipient has to open and reassemble themselves.
Common scenarios: combining a resume with a cover letter and reference letters into one application packet, merging scanned receipts into a single expense report, stitching together chapters or appendices of a document, or combining multiple signed contract pages that were scanned separately.
How to merge PDF files online — step by step
- Upload your PDFs — drag PDF files onto the upload zone or click to browse. Add up to 20 files at once.
- Set the merge order — files are listed in the order you added them. Use the up and down arrows to rearrange them until the sequence is correct; the number on the left shows where each file lands in the final document.
- Click Merge PDFs — pdf-lib combines every page from every file inside your browser. No data leaves your device.
- Download — click the Download button to save the combined PDF.
Does merging affect PDF quality?
No. This tool copies each source PDF's pages directly into the new document rather than flattening them into images and rebuilding a PDF around those images — a shortcut some online tools take that silently reduces text sharpness and makes text unselectable. Text stays selectable and searchable, vector graphics stay crisp at any zoom level, and embedded images keep their original resolution. The merged file size is roughly the sum of the inputs.
Merging PDFs on Windows, Mac, iPhone, and Android
| Platform | Built-in method | Limitation |
|---|---|---|
| macOS | Preview → drag one PDF's thumbnail into another | Only combines two at a time; fiddly for more than a few files |
| Windows 10/11 | No built-in merge tool | Requires third-party software or an online tool |
| iPhone / Android | No built-in merge tool | Requires an app or a browser-based tool like this one |
| Any browser | This tool | Up to 20 files, reorderable, no install |
For more than two or three files, or on Windows/mobile where there is no built-in option, a browser-based merge tool is the fastest route — no software install, works on any device with a browser.
Password-protected and encrypted PDFs
This tool cannot merge PDFs that are password-protected or encrypted — the merge will fail with an error naming the affected file. Remove the password first (Preview on Mac can do this via File → Export, or use Adobe Acrobat), then re-upload the unlocked file here.
Need to split, convert, or compress instead?
If you have a single PDF you need to pull pages out of as images, use PDF to JPG. To build a PDF from photos rather than combine existing PDFs, use Image to PDF. If your merged file needs to be smaller for email, most email providers cap attachments around 25 MB — check the file size shown next to the Download button after merging.
Privacy: your PDFs stay on your device
All processing runs entirely inside your browser using pdf-lib. Your files are never uploaded to any server — there is no upload step, no temporary server file, and no activity log. The merged PDF exists only in browser memory until you click Download, at which point it is saved to your device. Closing the tab clears everything.