The scanner fed the stack backwards: reverse PDF page order

The fix, step by step

1. Drop the backwards PDF on the tool above.
2. Under the page list, choose Reverse the order. The list now runs from the last page to page 1; check the first few rows.
3. Choose Apply and download the new file, named like scan-organised.pdf.

We tested it on a 3-page file (pages came out 3, 2, 1) and on a 500-page file: all 500 pages came out last to first in about half a second on our test machine. If you also need a page turned, choose Turn on its row before you apply; Reset puts the original order back.

Reverse several files at once

Organise takes 1 file at a time. Extract pages takes many, and it builds each new file in the exact order you type, ignoring numbers above the page count. So 1 list reverses every file up to 100 pages:

Extract pagesSelected pages to a new file. Free, runs on your device.Open

1. Drop all the backwards PDFs on Extract pages.
2. Copy this list and paste it into the Pages box:

100, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 89, 88, 87, 86, 85, 84, 83, 82, 81, 80, 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, 62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1

3. Click Extract and download the results as 1 zip.

Pages that do not exist are skipped, so on a 12-page scan the list becomes 12, 11, 10 down to 1. Each file is named in the order taken: a 3-page scan comes out as scan-pages-3_2_1.pdf, a longer one as scan-pages-12-to-1-reordered.pdf, so a reversed copy is never mistaken for the original. The 500-page test file, with a list from 500 to 1, took about 0.6 seconds.

For more than 100 pages, make a longer list in a spreadsheet: =TEXTJOIN(", ",TRUE,SEQUENCE(300,1,300,-1)) in Excel 365 or Google Sheets gives 300 down to 1. Change both 300s to your page count or anything above it, copy the cell, paste.

Which problem you have

Scans go wrong in 4 ways that look alike at first glance. Flip through the file once and match it to a row:

What you see, page by page	What happened	The fix
12, 11, 10 … 1	The stack went through last page first	Reverse the order in Organise
1, 2, 3 … but every page upside down	The stack went in head first	Rotate PDF, 180°, All
12, 11, 10 … 1, and upside down	Both at once	Reverse, then rotate 180°
Front 1, front 2, front 3, back 3, back 2, back 1	A double-sided stack scanned as 2 runs	Interleave, not reverse (see the last section)

Why the scan came out backwards

A document feeder pulls 1 sheet at a time, always the one at the feeding end of the stack. Whether page 1 or the last page goes through first depends on which way up the stack sits and where the feeder grabs it. A stack that came out of a printer face up has the last page on top, and loaded that way into a feeder that takes the top sheet first, it scans backwards.

The fix for next time is on the feeder itself: most have a small icon showing which way the pages go (face up or face down, top edge first). Load the stack to match the icon with page 1 where the feeder takes its first sheet, scan 2 test pages, and check the order before scanning 50. Some scanner apps also have a setting to reverse the order after scanning.

Reverse only part of the file

When the first pages are right and only the rest came out backwards (say pages 1 to 3 are a cover letter scanned separately, and pages 4 to 20 are the backwards contract), Organise can do it on a short file: choose Reverse the order, then move pages 1, 2 and 3 back to the top with their Up buttons. Each click moves a page 1 place, so on a longer file the list is quicker. Type the good pages first in Extract pages, then paste the list:

1-3, 100, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 89, 88, 87, 86, 85, 84, 83, 82, 81, 80, 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, 62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1

Each page appears once, in the first place you name it. Pages 1, 2 and 3 come first; when the list reaches 3, 2 and 1 again they are skipped. The result is 1, 2, 3, then 20 down to 4.

Backwards and upside down at once

Some feeders take the stack the wrong way round in both senses: last page first, and every page upside down. Fix it in 2 passes:

1. Reverse the order in Organise as above.
2. Drop the result on Rotate PDF, choose 180° and All, and download.

When every page needs the same turn, the order of the 2 passes does not matter. It does when only some pages are upside down: rotate by page numbers after reversing, because reversing changes which number each page has. The rotation is written into the page, not drawn as a turned copy, so the scan keeps its quality. The guide to organising PDF pages covers turning just a few.

Rotate PDFAll, odd/even or selected pages. Free, runs on your device.Open

What this cannot fix

Reversing cannot fix interleaving. If you scanned a double-sided stack as all the fronts, then turned it over and scanned all the backs, your file runs front 1, front 2, front 3, then back 3, back 2, back 1. That needs the fronts and backs merged alternately, which is a different job. The page list trick can do it on a short file (for 3 sheets: 1, 6, 2, 5, 3, 4), but you type every number by hand.

Neither route carries bookmarks, metadata or form fields into the new file, since both copy only the pages. For a scan that loses nothing. For a structured document with an outline, ask whoever made the file for a correct export. And if the scanner added blank backs between the pages, remove blank pages after reversing. More page jobs, from merging to numbering, are in the guide to organising PDF pages.