Unir PDF
Combina múltiples documentos PDF en uno solo de forma rápida y privada.
Click to select or drop multiple PDFs here
At least 2 files, up to 20
Merging does less than it sounds like: page objects from each PDF are copied into a new document, page numbers are recalculated, and the file is written out. Pages get copied, not the structure wrapped around them, so bookmarks, form fields, and any existing digital signature stop working afterward. A signature is a checksum over the whole file; rebuild the file and the check can't match. That's true of every merge tool, not just mine.
Order is set with two buttons, Move up and Move down. No drag-to-reorder, no thumbnail grid, so a long list takes a few clicks. Better you know that now than after you try dragging.
There are two size walls, not one: 50MB per file free (100MB Pro), 200MB across all files combined (300MB Pro), up to 20 files free (50 Pro). Twenty 30MB scans each clear the first wall and slam into the second.
FAQ
Does merging PDF files upload them to a server?
No. pdf-lib reads the pages, assembles the document, and writes the result inside your browser's memory. No upload request appears in the network panel, and merging works with your Wi-Fi switched off. You can confirm this yourself the same way as with any other tool on this site. The separate AI features do call DeepSeek, but only with text extracted locally, never the PDF itself.
Can I drag to reorder files when merging PDFs?
No. Reordering uses two buttons, Move up and Move down, one position per click, and there are no page thumbnails to preview what's inside each file. The dragging on this page only drops files into the drop zone; it doesn't sort them. The quickest approach is to add files in roughly the order you want, then nudge them with the buttons.
What is the file size limit for merging PDFs?
Three limits apply: 50MB per file (100MB on Pro), 200MB for all files combined (300MB on Pro), and 20 files (50 on Pro). The combined limit is the one people miss — twenty 30MB scans are each individually fine and still fail. The numbers are built around pdf-lib peaking at roughly 3-5x the file size in memory, which is a real browser constraint.
Do bookmarks and digital signatures survive a PDF merge?
Bookmarks and form fields are lost, and any existing digital signature becomes invalid. A signature validates the entire file, so once pages are reassembled the check can no longer match. Every merge tool behaves this way, Acrobat included — it isn't a bug here. If you're merging a signed contract, merge first and sign the result, or keep the signed original filed separately.
How does this compare to iLovePDF or Smallpdf for merging PDFs?
The real difference is that your files never leave your computer, and you can verify that yourself rather than taking my word for it. Honestly, they do far more than I do: OCR, batch jobs, cloud storage, collaboration. I'm one developer and I can't match that breadth. If you just need a few files joined and would rather not hand a contract to anyone, this is enough.