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Interleave PDFs

Merge two PDFs by alternating their pages (A1, B1, A2, B2…). Great for joining separate front-side and back-side scans.

First PDF (odd pages)

Drop the first PDF

fronts, in order

Select file
PDF

Second PDF (even pages)

Drop the second PDF

backs

Select file
PDF
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About Interleave PDFs

This solves a specific and irritating problem. You have a document printed on both sides and a scanner that only feeds one side at a time, so you scanned all the fronts, flipped the stack, scanned all the backs, and now hold two PDFs that need to become one correctly ordered document.

Interleaving alternates pages from the two files: first page of A, first page of B, second page of A, and so on. Because the back sides were scanned after flipping the stack, they usually come out in reverse order, so there is an option to reverse the second file as it is merged.

Getting this right by hand means dragging dozens of pages into position and is easy to get subtly wrong. Doing it as one operation removes the chance of an off by one error halfway through a long document.

Pages are copied at original quality with no re-encoding, and the two source files are left exactly as they were.

How to interleave pdfs

  1. Add both files

    Load the file containing the front sides first, then the one with the backs.

  2. Reverse the second if needed

    If the backs were scanned after flipping the stack, turn on the reverse option so they line up correctly.

  3. Merge and check

    Download the interleaved PDF and spot check a few pages to confirm the pairing.

Frequently asked questions

Why would the second file need reversing?

Because flipping a stack of paper reverses it. The last front becomes the first back, so scanning the flipped stack produces the backs in opposite order. Reversing during the merge corrects this.

What if the two files have different page counts?

Interleaving continues until the shorter file runs out, then appends the remaining pages of the longer one. Unequal counts usually mean a page was missed, so it is worth checking the source scans.

Can I interleave more than two files?

Not in one pass. Interleave two, then interleave the result with a third if you need to.

Does this work with scanned images rather than text PDFs?

Yes. Interleaving reorders pages regardless of whether they contain text or scanned images.