Interleave the pages of two PDFs

How to Alternate & Mix PDF

1. Add the file with the fronts. Drop in the PDF holding the odd-numbered pages — pages 1, 3, 5 and so on.
2. Add the file with the backs. Drop in the second PDF. Drag to reorder if it landed first.
3. Reverse the second file. Turn on Reverse for the stack of backs. Scanning them after flipping the pile puts them in reverse order, and this is what corrects it.
4. Mix and check page two. Save the mixed PDF, then look at page two. It should be the back of page one.

The problem this actually solves

Almost everyone who needs this arrives from the same predicament: a double-sided document and a scanner, or a phone, that only does one side at a time.

So you scan the whole stack face up and get a PDF of the odd pages. Then you turn the pile over and scan it again, and get a PDF of the even pages — but in reverse order, because turning a stack over reverses it. The last sheet is now on top, so its back is the first page scanned.

Interleaving the first file forwards with the second file backwards reconstructs the original document. That is the entire job, and the reverse toggle is not a refinement — without it the tool does not solve the problem it exists for.

Checking it worked in one glance

Look at page two of the result. If it is the back of page one, everything behind it is right too. If it is the back of the last sheet, the second file needed reversing and did not get it — turn Reverse on and mix again.

That single check is reliable because the failure is systematic rather than random. Interleaving either lines up or it does not; there is no arrangement where the first few pages are correct and the rest drift.

If the two scans have different page counts — the usual cause being a final sheet printed on one side only — the extra pages are kept and appended in order rather than the mix being truncated to the shorter file.

Other things worth interleaving

A translated document, alternating the original and the translation so each page faces its counterpart.

A score and its part, or a script and its stage directions, where two separately exported PDFs need to read as one alternating document.

Two halves of a document that were exported separately for a reason that has since stopped mattering — a covering letter set and a form set that need to be collated one-to-one rather than stacked.

More than two files works too. One page is taken from each in the order listed, so three files interleave three ways.

Why bookmarks are dropped here

Merging two PDFs end to end keeps each file's bookmarks and gives the result a branch per file, which is what makes a merged report navigable. Interleaving cannot do that honestly.

Once pages alternate, a bookmark branch named after a source file would point at every other page of the document — technically accurate, useless to read, and misleading about what the file now is. So no outline is written, and the merged result carries none rather than carrying a broken one.

If you need bookmarks on the mixed document, add them afterwards with Add PDF Bookmarks, where they can describe the reconstructed document rather than the two scans it came from.

Frequently asked questions