This is the inverse of interleaving. It takes one document and produces two: pages 1, 3, 5 and so on in the first, pages 2, 4, 6 in the second. The reason to want that is almost always printing.
Double-sided printing on a one-sided printer
A printer without a duplex unit can still produce a double-sided document with two passes. Print the odd file, take the stack out, put it back in the tray the other way up, then print the even file onto the backs.
The part that takes a try or two is working out which way to reload the paper — it depends on whether your printer feeds face-up or face-down. Test with a four-page document before committing a hundred sheets. Write "1" on the first sheet before the second pass so you can see exactly what happened.
You may also need to reverse the even file first. If your printer stacks output face-up, the pages come out in reverse order, so the backs need to be printed backwards to line up. The page reverser handles that.
Other uses
- Separating the fronts and backs of a scanned document so each can be checked or processed on its own.
- Discarding the backs of a document where every even page is blank — a common result of scanning single-sided originals in duplex mode.
- Splitting a booklet into the two passes a print shop asked for.
- Isolating alternating content, such as a bilingual document with each language on facing pages.
Odd and even mean the printed page numbers
Worth stating explicitly because it is a genuine source of confusion. "Odd" means pages 1, 3, 5 as your reader numbers them, which are positions 0, 2, 4 counting from zero. If the document has its own printed page numbers that differ — a report where page 1 of the text is the fourth sheet — those are ignored. What matters is the position in the file.
Nothing is altered
Both output files are built by copying page objects, so text stays selectable, scans keep their original bytes and vectors stay sharp. A document with an odd number of pages gives an odd file one page longer than the even one, which is correct and expected.
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Blank backs are worth checking for
Scanning single-sided originals in duplex mode produces a document where every even page is blank. Splitting it this way gives you an even file of nothing but empty pages, which you can discard, and an odd file that is the real document. It is a quick way to clean up a scan that doubled in length for no reason.