How to merge PDF files
- Add your PDFs. Click the dashed box above or drag files onto it. You can select several files at once and add more later – each new batch is appended to the end of the list.
- Check the order. Files are joined from top to bottom exactly as they appear in the list. Use the × button to remove a file you added by mistake.
- Fix the order if needed. There is no drag-to-reorder, so remove any file that is out of place and add it again at the end. Adding files one at a time gives you full control, because the order of a multi-file selection depends on your system's file dialog.
- Press Merge PDFs. At least two files are required. The progress bar advances as each file is read and copied.
- Download the result. The combined document is saved as
merged.pdf; rename it to something your recipient will recognize.
What happens when you press Merge
The merge runs inside this browser tab using pdf-lib, an open-source JavaScript library for creating and modifying PDF documents. Each file is read from your disk into memory with the browser's FileReader API and parsed by pdf-lib. The tool then creates a new, empty PDF and copies every page of every input file into it, in list order.
Copying happens at the level of PDF objects: the drawing instructions of each page, together with the fonts and images it uses, are transferred as they are. Nothing is re-rendered or re-compressed, which is why text stays selectable and searchable, vector graphics stay sharp and photos keep their original quality. The finished document is written into memory and offered as a download – your files never travel over the network.
What is kept and what is not
- Kept: page content, embedded fonts and images, the size and orientation of every page, page rotation, and comments or highlights attached to pages.
- Not kept: bookmarks (the outline panel in your viewer), the title, author and subject fields of the source files, page labels and file attachments. The merged file gets its own fresh document properties.
- May stop working: fillable form fields, because the form definition belongs to the source document rather than to its pages, and links that jump to another page of the original document. Links to web addresses normally keep working.
Tips for a tidy merged document
- Number your files first. Names like
01-cover.pdfand02-report.pdfsort into sequence in the file dialog, and a file that lands in the wrong place is easy to spot in the list. - Flatten filled-in forms. If an input is a completed form, open it in your PDF viewer and use Print → Save as PDF first. The answers then become ordinary page content and survive the merge.
- Mixed page sizes are fine. An A4 page next to a US Letter page or a landscape table stays exactly as it is. When printing, "Fit to page" scales each page separately.
- Watch the total size. The result is roughly the sum of its inputs, because a font used in several source files is copied once per file. If it must fit an email limit, read how to make a PDF small enough to email.
When merging PDFs saves time
- Sending one application package – CV, cover letter and certificates – instead of five separate attachments.
- Combining monthly statements or invoices into a single file for your accountant.
- Joining two halves of a document after the scanner stopped partway and saved two files.
- Putting a signed and scanned signature page back into the full contract.
Limitations and alternatives
- Password-protected PDFs cannot be merged. pdf-lib cannot decrypt encrypted files, so the tool stops with an error that mentions encryption. If you know the password, save an unprotected copy in your PDF viewer (where the document's permissions allow it) and merge that.
- Memory is the size limit. All inputs and the output are held in memory at the same time. Computers usually cope with files of many tens of megabytes; phones and tablets run out sooner. If a big merge fails, combine a few files at a time and then merge the partial results.
- Whole documents only. To use just some pages of a file, extract them with Split PDF first.
- Digital signatures do not carry over. Pages copied into a new document are no longer covered by the original signature.
- Need bookmarks or working forms? Desktop software such as Adobe Acrobat can merge bookmarks, and the free command-line tool qpdf (
qpdf --empty --pages a.pdf b.pdf -- merged.pdf) is good at keeping form fields working.
Frequently asked questions
Is there a limit on how many PDFs I can merge?
There is no fixed limit on the number of files or pages. The practical limit is your device's memory, because every file is loaded into the browser at once. If a very large merge fails on a phone, combine the files in smaller groups and merge the results.
Are my PDFs uploaded to a server?
No. The files are read and combined by JavaScript running in your browser, and the merged file is created on your device. You can check this in your browser's developer tools: the Network tab shows no request carrying your files when you press Merge PDFs.
Can I merge PDFs with different page sizes or orientations?
Yes. Every page keeps its own size and orientation, so portrait and landscape pages, or A4 and US Letter pages, can sit side by side in the merged file.
Why does the merge stop with an error about encryption?
At least one file is encrypted, usually because it is password-protected. The library used here cannot decrypt PDFs, so remove the protection in a program where you can enter the password and try again.
Will bookmarks and form fields be kept?
Bookmarks are not copied, and fillable form fields may stop working. Page content, images and comments are kept. If the forms are already filled in, print them to PDF first so the answers become part of the page.
How do I change the order of the files?
Files are merged in the order shown in the list. Remove a file that is in the wrong position with the × button and add it again at the end, or number the file names before you start.
Related tools
- Split PDFExtract only the pages you need before or after merging.
- Compress PDFRe-save a PDF more compactly and compare the size.
- JPG to PDFTurn photos or scans into a PDF that you can then merge.
- Add WatermarkStamp DRAFT or CONFIDENTIAL across the combined document.
Further reading: How to make a PDF small enough to email.