The fold is what scrambles the page order
Fold a stack of paper in half and staple through the crease and you have a saddle-stitched booklet: a programme, a zine, a short manual, a school newsletter, a chapbook. The awkward part is that the fold destroys any relationship between the order pages are printed in and the order they are read in. On the outermost sheet, the right half is page 1 and the left half is the very last page, because once the stack is folded that left half wraps around to become the back cover.
This tool applies the standard imposition. For a booklet of n pages, sheet k carries page n minus 2k plus 2 on the left of its front and page 2k minus 1 on the right, then page 2k on the left of its back and page n minus 2k plus 1 on the right. For an eight-page booklet that gives sheet one holding pages 8 and 1 on the front and 2 and 7 on the back, and sheet two holding 6 and 3 on the front and 4 and 5 on the back. Every pair on the same side of a sheet adds up to n plus one, which is a quick way to check a printed result by eye.
Working the same arrangement out by hand is not hard so much as unforgiving. One transposed pair and the booklet reads out of order from that point on, and you only discover it after the paper is folded.
Sheets come in fours, so the count gets rounded up
Because one folded sheet contributes exactly four booklet pages, the total has to be a multiple of four. A 10-page PDF needs two more positions to reach 12, a 9-page PDF needs three, and a 13-page PDF also needs three, to reach 16.
The tool computes that padding itself. Those extra positions do not exist as pages anywhere; they are simply positions with no source page behind them, so the corresponding half of a printed sheet comes out blank. You never have to prepare the file first, and the blanks land where convention puts them, at the end of the booklet.
From PDF to a stapled stack
- Drop your PDF onto the box above, or use Choose a file to pick it. One file at a time, and
only
.pdfis accepted. - Set Paper size to A4 or US Letter, matching the paper actually in the tray.
- Click Print PDF as Booklet and watch the progress bar work through the sheets.
- Download the result, then print it double-sided so that the reverse of each sheet is mirrored across the fold line.
- Fold the whole stack in half together and staple twice along the crease.
Two habits save paper here. Print one sheet first and fold it to confirm your duplex setting before sending forty. And if the document is assembled from several files, combine them with Merge PDF first, since the padding is calculated from the page count of the single file you feed in.
Landscape sheets and contain-fitted halves
The output sheets are the full size of the paper you chose, turned landscape, because two pages side by side are wider than they are tall. Each half is therefore half the paper’s long side wide and its full short side tall, and each source page is scaled down to fit inside that box with its proportions intact and centred within it. There is no margin reserved at the fold: the halves meet at the exact centre of the sheet.
For a portrait A4 source on A4 paper that works out neatly, and each page lands at close to A5. A portrait Letter source on Letter paper fills the half’s width and stops short of its height, so the printed page is a little squatter than A5 with white above and below. Source pages that are already landscape are the case to watch. Nothing is rotated, so a wide page is squeezed until its width fits half a sheet and ends up small, with white space above and below. Mixed-orientation documents behave the same way page by page, which is worth knowing before you print a hundred of them.
When the fix belongs to another tool
If the booklet reads correctly but one page is in the wrong place, that is a source-document problem rather than an imposition problem, and Reorder PDF Pages moves a single page to a new position per run. If your document has pages stored sideways, Rotate PDF can turn them by 90, 180 or 270 degrees across the whole file or a page range before you impose it.
And if what you actually want is fewer sheets rather than a bound booklet, you want N-up PDF instead: it places 2, 4, 6 or 9 pages on each sheet in ordinary reading order, across-then-down or down-then-across, which is right for handouts and lecture slides and wrong for anything you intend to fold. Imposition and saving paper look similar in the output and are not the same operation.
Everything above runs on your own device with the pdf-lib library. The file is read into memory, a new document is drawn, and the result goes to your downloads folder without a network round trip, which matters for the kind of thing that usually gets bound: internal meeting materials, a manuscript draft, an event programme with names in it.
