How to use the merge pdf
- Choose two or more PDF files with the picker, or drop them onto the box. You can add more files later and they join the end of the list.
- Check the page count and size shown for each file. Use Up and Down to change the order, or Remove to take a file out of the list.
- Select Merge and download. The combined file is saved as merged.pdf on your device.
- Open merged.pdf and scroll through it to confirm the order before you send or archive it.
How the merge works in your browser
This tool reads each PDF into your browser memory, copies every page into a new document with the open source pdf-lib library, and saves the result as a new file. The copy keeps each page as it was: the same size, rotation, text, images and fonts. Files are handled one at a time, so memory use stays close to the size of the output rather than the sum of several copies.
Your files are never uploaded. SumPanda does not receive them, store them or see their names. You can verify this in the network panel of your browser: adding and merging files produces no request that carries them.
Limits you should know about
A browser tab has a limited amount of memory, so the tool sets clear caps and tells you which one you hit instead of failing partway through.
- 25 MB per file. A larger file is skipped with a message that names it.
- 100 MB across all files in one merge.
- 500 pages in total. The page count is read when you add a file, so you find out before you start.
- Encrypted or password-protected PDFs are rejected. The tool does not try to guess or remove passwords.
What a merge keeps and what it can lose
Page content is preserved. Document-level features that belong to a single source file are not carried over reliably. Bookmarks (the outline panel), named destinations, form fields shared across files, tags used for accessibility, and digital signatures may be dropped or invalidated, because a signature covers the exact bytes of the original file. If you need a signed document to stay valid, keep the original and do not merge it.
Links inside a page that point to another page of the same file can stop working after a merge. Links to websites are normally kept.
Tips for a clean result
Name your files with a leading number such as 01-cover.pdf and 02-report.pdf before you add them. The picker often lists them in name order, which saves reordering.
If the finished file is too big to email, merge first and then check the size. Merging does not recompress images, so a merged file is roughly the sum of its parts. To reduce size, rebuild the pages as images with the PDF to image converter and the image to PDF tool, which trades sharp text for a smaller file.
To remove pages from a merged file, use the organize PDF pages tool. To pull a few pages out of a large file first, use the split PDF tool.
Assumptions and limits
- Files are processed entirely on your device. Nothing is uploaded, and the tool has no account or history.
- Only PDFs that your browser can open without a password are supported. Damaged files are reported, not repaired.
- Signatures, bookmarks and tagged-PDF accessibility structure are not guaranteed to survive a merge.
- The limits (25 MB per file, 100 MB total, 500 pages) are set for typical phones and laptops. A very complex page can still be slow.
- The output keeps the pdf-lib default document information. Titles and authors from the source files are not copied over.
Frequently asked questions
Are my PDFs uploaded when I merge them?
No. The files are read by your browser and merged in its memory. No request carries your documents anywhere, and SumPanda has no server that could receive them.
Why does it say my PDF is password protected?
The file has an encryption setting, and this tool cannot open encrypted PDFs. It also does not try to crack passwords. Open the file in the program you normally use, save an unprotected copy if you are allowed to, and add that copy instead.
Can I change the order after adding the files?
Yes. Each row has Up and Down buttons that work with a keyboard or a screen reader, and the position is announced after each move. You do not have to drag anything.
Will the merged PDF be bigger than the originals combined?
It is usually close to the sum of the originals. Pages are copied as they are, so images are not compressed again, and shared resources such as fonts may be stored once per source file.
What happens to bookmarks and form fields?
Page content is kept, but bookmarks, document-level form logic and signatures may not carry over. Check the result if your files rely on them.