The short answer
A scanner without a duplex feeder gives you two files: every front, then every back, and the backs are usually in reverse order. Alternate and Mix interleaves them into the right sequence in one pass, reversing the second file if needed.
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Step by step
- Scan the fronts, then flip the whole stack and scan again Do not reorder the stack between passes. Flipping it as one block is what makes the backs land in predictable reverse order.
- Add both files, fronts first The first file supplies the odd pages, the second the even ones.
- Reverse the second file if the backs came out backwards Flipping the stack means the last sheet was scanned first. The option to reverse is there for exactly this — check page 2 is the back of page 1 before saving.
- Check a middle sheet, not just the first The first pair is almost always right even when the rest are wrong. Verify a sheet from the middle to be sure the interleave held.
- Delete any trailing blank An odd number of sheets leaves one blank back at the end. Remove it so the document ends where the content does.
Questions
My backs are upside down as well. Can that be fixed?
Yes — rotating the even pages by 180 degrees corrects it, and the rotation is written into the file so it is right everywhere.
What if I have an odd number of sheets?
The last sheet has no back, so you get one trailing blank page. Delete it after interleaving.
Does this work for a double-sided form with a blank back?
It does, but consider whether you want the blanks at all. If the backs are empty, a single-sided scan is the cleaner document.
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