How to Impose a PDF for Saddle Stitch
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What imposition is
Imposition maps logical reader pages onto physical sheets. In saddle-stitch 2-up work, each side of a sheet holds two reader pages, left and right of a fold. The outermost sheet carries the cover and the last page. Inner sheets nest. You fold the whole pile once. That is one signature.
This product does not do perfect bind, spiral, or multiple signatures. Perfect bind stacks folios at a spine glue edge; the page order is not this formula. If you need that bind, do not use these sheets.
Why the count must be a multiple of 4
Each sheet has four slots: front left, front right, back left, back right. A 5-page PDF cannot fill those slots without empty places. We never drop your pages. We append blank pages until N is a multiple of 4. A one-page PDF becomes four pages: your page plus three blanks. A five-page PDF becomes eight.
8-page order
For N=8, sheet 0 (outer) is 8|1 on the front and 2|7 on the back. Sheet 1 (inner) is 6|3 then 4|5. Page 1 is the front cover because it sits front-right on the outer sheet. See the 8-page booklet page order worked example.
16-page order
Four sheets. Outer: 16|1 and 2|15. Then 14|3 and 4|13. Then 12|5 and 6|11. Innermost: 10|7 and 8|9. Full table on the 16-page booklet imposition page. The same formula scales to 20, 24, and beyond.
Run it here
You do not have to fill the table by hand. Open the PDF booklet maker, load the file, preview Sheets / Reader / Spreads, and export. Creep and gutter are optional.
Prefer a worked example first? Walk through the 8-page booklet page order or the 16-page booklet imposition, or use the live saddle stitch page order calculator to see Front/Back slots on your own PDF.
Questions
Why must the page count be a multiple of 4?
Each sheet has four slots (front left/right, back left/right). If your PDF is not a multiple of four, blank pages are appended at the end until it is. Source pages are never dropped.
Does this work for perfect bind?
No. Perfect bind stacks folios at a glued spine; the page order is not this saddle-stitch formula. This tool builds one nested signature for folding and stapling through the spine.