Combine two PDFs, alternating pages
You scanned the fronts of a stack, flipped it, scanned the backs — and now the odd pages live in one PDF and the even pages in another. This page weaves them back together: page 1 from file A, page 1 from file B, page 2 from A, page 2 from B… with the crucial option to walk the second file backwards, because a flipped stack scans in reverse order.
The alternate & mix option is pre-enabled below, with “second file is back-to-front” already checked — the configuration that fixes the standard single-sided-scanner workflow. Uncheck it if your even-page pass came out in forward order.
Preset: alternate & mix is on, second file reversed (the usual duplex case).
Drop your PDFs here
Add two or more files — or click to browse. Processed on your device, never uploaded.
How it works
- Drop the odd-pages file first, then the even-pages file.
- Leave “alternate & mix” on; keep “back-to-front” checked if the backs were scanned by flipping the stack.
- Click “Merge 2 PDFs”.
- Download — pages come out 1, 2, 3, 4… in true reading order.
Which order did your scanner produce?
Quick test: open the even-pages file and look at its first page. If it’s the last page of the document (the highest even number), your stack was flipped and the reverse option is correct — this is the overwhelmingly common case. If its first page is page 2, your scanner or software already reordered the backs — uncheck “back-to-front”.
Unequal counts are handled sensibly: if the files differ in length (an odd total number of pages means the fronts file has one extra), the leftover pages are appended in order once the shorter file runs out.
Good to know
- Scan the fronts first, backs second, and drop the files in that order — the tool interleaves starting with the first file.
- A blank final page after merging means the back of your last sheet was blank — remove it with the last-page preset.
Frequently asked questions
The merged pages are in the wrong order. What went wrong?
Almost always the reverse toggle. The signature of a missing reverse (on a 6-page document): 1, 6, 3, 4, 5, 2 — odd positions counting up, even positions counting down. Toggle “back-to-front” and re-merge. If the order starts right but drifts later, the two passes probably don’t contain the same sheets — check for a double-feed in one of the scans.
Can I interleave three or more files?
Alternate & mix here is built for the two-file duplex case. With three or more files loaded, the tool merges them in sequence instead. True N-way interleaving is rare enough that we’d rather keep this page simple and correct.
My scanner has a duplex mode. Should I still use this?
If your scanner scans both sides in one pass, you don’t need this page — it already outputs reading order. This tool is for single-sided scanners and the flip-the-stack technique.