Initializing Secure Environment…
Initializing Secure Environment…
Combine two or more PDFs by alternating their pages rather than joining them end to end. The classic use is a document scanned on a single-sided feeder: you scan all the fronts, flip the stack, scan all the backs, and end up with two files that need zipping together — with the backs in reverse order. Turn on Reverse for that file and the pages come out in sequence. Files of unequal length are handled cleanly, and nothing is uploaded.
To interleave two PDFs, take one page from each file in turn instead of appending one after the other. On ihatepdf, add both files, and if the second was scanned in reverse — as a stack of backs usually is — turn on Reverse for it. The output alternates page 1 of the first file, page 1 of the second, page 2 of the first, and so on, reuniting fronts and backs in the correct order.
Sheet-fed scanners without a duplex unit are still everywhere, and they all create the same problem. You feed the stack once to capture the fronts, turn the whole pile over, feed it again to capture the backs — and now you have two PDFs that interleave rather than concatenate, with the second one in reverse order because turning a stack over reverses it. Doing this by hand in a page organiser means dragging every second page into position, which for a forty-page document is both tedious and easy to get subtly wrong. Alternating with a reverse toggle turns it into two clicks, and unequal counts are handled automatically for the case where the last sheet was blank on the back.
Beyond duplex scanning, alternating pages is how you build a bilingual document with each translated page facing its original, assemble a comparison set where each revised page sits next to the version it replaced, or reunite a set of forms with the set of continuation sheets that belongs with them. Anywhere two documents are parallel rather than sequential, interleaving is the operation you actually want, and a plain merge is the one that will quietly produce the wrong thing.
Sheet-fed scanners without a duplex unit are still everywhere — in home offices, small practices, schools and the back rooms of organisations that bought a good scanner once and never replaced it. They all create the same problem. You feed the stack to capture the fronts, turn the whole pile over, feed it again to capture the backs, and now you hold two PDFs that need to interleave rather than concatenate, with the second one in reverse order because turning a stack over reverses it. Doing this by hand in a page organiser means dragging every second page into position, which for a forty-page document is both tedious and easy to get subtly wrong in a way you only discover later. Two files, one Reverse toggle and one click replaces the whole exercise.
The failure mode with interleaving is not a crash, it is a document that looks plausible and is wrong — pages in the right count but the wrong sequence, discovered weeks later by whoever has to read it. That is why the resulting order is shown as an explicit sequence before anything is built: A1 B3 A2 B2 A3 B1 tells you at a glance that file A is running forwards and file B backwards, which is exactly what a duplex scan should look like. If it reads A1 B1 A2 B2 you have forgotten the Reverse toggle, and you can see that in a second rather than after printing forty pages.
Beyond duplex scanning, alternating pages is how you build a bilingual document with each translated page facing its original, assemble a comparison set with each revised page next to the version it replaced, reunite a set of forms with the continuation sheets that belong to them, or lay out a deck so each slide is followed by its notes page. Anywhere two documents are parallel rather than sequential, interleaving is the operation you want and a plain merge is the one that will quietly produce something unusable.
It takes one page from each file in rotation. With two files it produces A1, B1, A2, B2, A3, B3 and so on, rather than the whole of A followed by the whole of B, which is what a normal merge does.
Scan all the fronts into one PDF, flip the whole stack over and scan all the backs into a second. Add both here, switch on Reverse for the backs, and interleave. The backs are consumed from the last page forwards, which is the order they were captured in.
That is fine. When one file runs out the others carry on, so the remaining pages are simply appended in order.
Yes. Add as many as you like and one page is taken from each in turn, following the order you arrange them in.
Merging concatenates: everything from the first file, then everything from the second. Interleaving alternates between them page by page. If you want one document after another, use Merge PDF.
No. Pages are copied across intact — nothing is re-encoded, re-compressed or rasterised.
No. The interleave runs in your browser with pdf-lib, so your documents stay on your device.
Scan all the fronts into one PDF, turn the whole stack over and scan all the backs into a second. Add both files here, switch on Reverse for the backs, and interleave. The backs are consumed from the last page forwards, which is the order they were captured in.
Because turning a stack of paper over reverses it. The sheet that was on top is now on the bottom, so the feeder captures the back of the last page first. Reversing that file undoes the flip. If your scanner ejects face-up rather than face-down the backs may already be in order, which is why Reverse is a toggle rather than something applied automatically.
All of them describe the same operation. Sejda calls it Alternate & Mix, PDF24 and others call it Alternate Merge, PDFsam calls it Mix, and a lot of documentation just says interleave. If you arrived looking for any of those, this is the tool.
That is handled. When one file runs out the others carry on, so the remaining pages are appended in order. With a duplex scan an uneven count usually means the final sheet was blank on the back.
Yes. Add as many as you like and one page is taken from each in turn, following the order you arrange them in. Three files produce A1 B1 C1 A2 B2 C2 and so on.
Merging concatenates — the whole of the first file, then the whole of the second. Interleaving alternates between them page by page. If you want one document after another, use Merge PDF.
No. Pages are copied across intact, so scan quality, OCR text layers and file size are all unaffected.
More essential pdf tools — all free, no upload.
Was this tool helpful? Rate it
Tap a star to rate.