How to Interleave Pages from Two Scanned PDFs (Collate Guide)

If your scanner doesn't do duplex, you end up with two PDFs: one with the odd pages (1, 3, 5…) and one with the even pages (2, 4, 6…). To interleave them into a single correctly ordered document, use Zro7 Collate PDF.

The classic scanner workflow

1. Scan the fronts of every page into odd.pdf.
2. Flip the stack, scan the backs — but they come out reversed: page N, N-2, N-4… in even.pdf.
3. In Collate PDF, drop odd.pdf as "A" and even.pdf as "B".
4. Toggle Reverse B so the even pages count back up correctly.
5. Download the interleaved PDF.

How interleaving works

Collate zips the two page lists together: A₁, B₁, A₂, B₂, … If B was scanned backwards (which duplex-less scans usually are), reversing B first gives the right physical order. If the two stacks have different page counts, the extra pages from the longer stack are appended at the end.

Fixing common issues

• Some backs are upside down — rotate with Rotate PDF before collating.
• One accidental blank page — remove with Delete Pages.
• Final file is huge — run Compress PDF and, if it's mostly text, PDF OCR to add a text layer.