How to Separate Odd and Even Pages From a Scanned PDF
Here's a scan that goes wrong in a specific, recognisable way. You feed a double-sided stack through a scanner that only reads one side, flip the whole pile, and feed it again. What you get is every front page followed by every back page - all the content, in an order nobody can read. The Extract Odd/Even Pages tool is the first step out of it.
How to tell this is what happened
Look at the second page of the file. In a correctly scanned document it's the back of page one. In this situation it's the front of sheet two, and the backs don't start until you're halfway through. A twenty-sheet document scans as pages 1 to 20 being the fronts and 21 to 40 being the backs, usually in reverse order because of how the stack was flipped.
Separating the two sets
Open the tool and choose your PDF. Pick odd or even pages, and you get a new document containing just that set. Run it twice and you have the fronts and the backs as two files.
That's the useful halfway point. You now have two clean sets rather than one unusable document, and whichever one came out reversed can be fixed on its own.
Putting the document back together
Once the two sets are in the right order, combine them with the Merge PDF tool and interleave the pages with the PDF Page Reorder tool. It's a few steps, but it's considerably faster than rescanning a long document, and nothing is lost in the process.
If the backs are blank - a single-sided document scanned on a double-sided setting - skip all of that. Just extract the odd pages and throw the rest away.
Check which set came out reversed
When a stack is flipped and fed through again, the second pass usually reads the sheets in the opposite order - so the backs come out last page first. Getting this wrong is the main reason a rebuilt document still does not read correctly.
The quickest check is to look at the first page of your even set. If it belongs with the last page of the odd set rather than the first, that set is reversed and needs turning around before you interleave anything.
It is worth doing this check before merging rather than after, because spotting it in a 40-page combined document is considerably harder than spotting it in two clean halves.
Common questions
Which pages count as odd?
Position in the file, counting from 1. The first page is odd, the second even, regardless of any numbers printed on them.
Does this work on documents that aren't scans?
Yes. The tool splits by position, so it works on any PDF.
What if my scanner produced the backs upside down?
That happens when the stack is flipped the wrong way. Rotate that set by 180 degrees with the Rotate PDF tool before combining.
Can I just rescan instead?
Often quicker for a short document. For anything long, separating and reordering is usually faster than feeding the stack through twice more.
Got a double-sided scan in the wrong order?