Interleave Two PDFs - Free Online Browser Tool

Alternate pages from two documents for duplex printing or read-alongside sets.

Two documents that have to be read together — a question paper and its answer sheet, or a contract and its translation — are almost impossible to keep aligned once they are printed separately. Interleaving builds a single document whose pages alternate, so every sheet of paper carries both halves side by side.

This interleave two pdfs utility runs completely inside your web browser. Your document is opened locally and processed on your own device using JavaScript and WebAssembly, so your file is never uploaded to any server. There is no signup, no watermark and no limit on how many documents you can handle.

  • 100% client-side - files never leave your device
  • Instant processing, no upload wait
  • Works on desktop, tablet and mobile
  • Free forever, no account required

Common next steps: Merge PDFs, Alternate Merge (Duplex), Merge Selected Pages, Add Extra Margins.

How to Use the Interleave Two PDFs Tool

Four steps, and the whole thing runs locally on your own device.

  1. Add both documents

    Select exactly two PDFs. Order matters: the first file is A, the second is B.

  2. Choose the page order

    Alternating gives A1, B1, A2, B2. In blocks gives all of A then all of B. Cover mode treats B1 as a front cover and holds A1 to the back.

  3. Process the pair

    Pages are copied across unchanged, so nothing is re-rendered and quality is untouched.

  4. Download the combined file

    Print duplex, flip on the short edge, and the two documents read together.

Frequently Asked Questions

What happens if one document is longer than the other?

The shorter one simply stops contributing once its pages run out. Nothing is invented to pad it out — a blank filler page would be worse than a shorter document, because it would silently renumber everything after it.

Does interleaving reduce quality or file size?

Neither. Page objects are copied across exactly as they are, so text stays selectable, images stay sharp and the file size is very close to the sum of the two inputs.

Which order do I want for duplex printing?

Alternating, and then flip on the short edge. That puts A1 and B1 on the front and back of the same sheet rather than on facing sheets.

Can I interleave more than two documents?

Not in one run. Run it twice and merge the results if you need three, though beyond two the alternating order stops being intuitive to follow.

Does this renumber or restyle anything?

No. Existing page numbers and footers stay exactly where they were, which is worth knowing if either document already carries its own pagination.