Rebuild duplex pages from two one-sided scans

Your feeder scans one side only — fronts in one PDF, backs in another (often reversed). Interleave them back into one document.

Tools used in this guide

The job

Scanning a double-sided document on a single-sided feeder gives you two files: all odd pages, then all even pages — usually in reverse order since the stack flips. Reading them means mentally re-shuffling two PDFs.

Interleave

Drop the fronts PDF and the backs PDF, tick 'reverse document B' if the backs came out last-page-first (the usual case). Output is A1, B1, A2, B2… — one document that reads front-back-front-back like the original.

If page counts differ, leftover pages from the longer document append at the end — check the page count summary.
Run a quick visual pass after merging: a blank back side should appear as a blank page, not shift the alignment.

Worked example

A 20-page duplex contract scanned as fronts.pdf (pages 1,3,5…19) and backs.pdf (pages 20,18,16…2 — feeder order). Interleave with B reversed produces the original 1–20 sequence.

Where it stops

Strict alternation only — it can't auto-detect which file has the fronts, and it doesn't delete blank pages afterward (use the blank-page remover if needed). Each input is limited to 25 MiB and 200 pages; signed and encrypted PDFs are refused.