Guide
Unir PDF: what it does and how to use it
PDF merge builds one PDF from several PDFs, in the order you choose. It is the straightforward way to combine a cover letter with a contract, stitch scanned pages that were saved as separate files, or assemble a handout from a few exports.
Add two or more PDFs, then move each file up or down until the list matches the page order you want. The merge copies pages in that sequence into a new document and downloads it. The originals stay on your device, and the work happens in the browser — the PDFs are not uploaded to be combined on a server.
Page content is preserved as PDF pages, not re-rendered as images, so text remains text. The tool does not reorder pages inside a single file; it orders whole files. If one PDF is in the wrong internal order, split or fix that file first, then merge.
How to use it
- 1
Drop at least two PDFs
The drop zone accepts PDF files and you can add more in a second drop. Non-PDF files are rejected.
- 2
Put the list in reading order
Use the up and down controls on each row. The top file becomes the start of the merged document.
- 3
Remove anything that should not be included
The remove control drops a file from the list only. It does not delete the original from your computer.
- 4
Merge and download
Click the merge button. You need at least two PDFs. The browser builds one file and downloads it.
Good uses
- Joining a signed page with the rest of an agreement.
- Combining several scanned chapters into one document.
- Building a single attachment from a proposal, an appendix, and a price sheet.
- Putting exported slides and a notes PDF into one handout.
Tips
- Name files so the list is obvious, then still check the order before you merge. File name order and visual order are not the same thing.
- If you only need pages 2–4 of one file, split that range out first, then merge the extract with the other documents.
- Very large image-heavy PDFs use memory in the tab. Close other heavy tabs if a big merge feels slow.
- Open the download and flip through the first and last pages. A reversed row is easier to catch before you send the file.
Limits to know
- At least two PDFs are required. A single file has nothing to merge with.
- Password-protected PDFs that the browser cannot open will fail. Unlock them in a tool that knows the password first.
- This does not edit text, compress images inside the PDF, or add page numbers.
Questions
Are my PDFs uploaded?+
No. pdf-lib runs in the browser. The merged file is created locally and downloaded.
Can I drag rows to reorder?+
Reordering uses the up and down buttons on each file, not drag and drop.
Will fillable form fields survive?+
Pages are copied into a new document. Interactive forms, signatures, and some annotations can behave differently after a merge. Check the result if the PDF is a live form.
Is there a page limit?+
There is no fixed page cap. The practical limit is how much memory your browser will spend on the files you added.