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My scanner is single-sided, so I scanned all fronts, then all backs. How do I put the pages back in front, back order?

Merge the fronts file and the backs file into one, then open it in the reorder tool. For three sheets, the merged file holds fronts 1, 2 and 3, then the backs on pages 4, 5 and 6 in reverse, so you arrange them as 1, 6, 2, 5, 3, 4 and check the “New order” line before downloading.

Published · 3 min read

Why the backs come out reversed

Scanning the fronts of a three-sheet stack gives a file with sheet 1, then 2, then 3. Then you flip the whole stack over to scan the backs, which puts sheet 3 on top, so the backs file comes out as the back of sheet 3, then 2, then 1. That is why the order you need is not a simple swap but an interleave of one straight half and one reversed half.

Check this in your own file first, because some scanners feed in a way that leaves the backs in straight order. Look at the first thumbnail of the backs: is it the back of the first sheet or the last?

Step one: merge the two files

Open Merge PDFs, add the fronts file first and the backs file second, and download the result. With three sheets you now have a 6-page file.

Step two: reorder the easy way

Instead of working out positions in the middle of the file, use each page's move-to-end button in the order you want the final file to have. Every page you press goes to the back of the line, so after the last press the file reads correctly from the start.

  1. Open Reorder PDF pages and choose the merged file.
  2. Press “Move page 1 to end”: the front of sheet one.
  3. Then “Move page 6 to end”: the back of sheet one.
  4. Then page 2, then 5, then 3, then 4, each to the end.
  5. Check the “New order” line: it should read 1, 6, 2, 5, 3, 4. Then press “Download in new order”.
Worked example

Three sheets: the merged file has pages 1, 2 and 3 for the fronts and 4, 5 and 6 for the backs, where 4 is the back of sheet 3 and 6 the back of sheet 1.

The order you need: 1, 6, 2, 5, 3, 4.

With four sheets the file has 8 pages and the order is 1, 8, 2, 7, 3, 6, 4, 5.

The general rule for any number of sheets

With n sheets the merged file has 2n pages. The order alternates between the start and the end of the file: page 1, then 2n, then 2, then 2n minus 1, and so on until the numbers meet in the middle. Write the sequence on paper before you start pressing, because a slip in the middle of 20 pages is harder to spot.

  • If your scanner leaves the backs in straight order, the sequence for three sheets becomes 1, 4, 2, 5, 3, 6.
  • Blank backs stay as white pages in the file. Delete them after reordering if you do not need them.

Common questions

Can I drag with the mouse instead of using buttons?

Yes on a computer, but the buttons are more precise on long files, and they are the only way on touch screens.

Will the backs be upside down?

That depends on how you flipped the stack. Reordering does not change page orientation, so rotate any upside-down pages afterwards.