How do I combine odd and even page scans into one PDF?

Add the PDF of odd (front) pages as file A and the even (back) pages as file B, keep "B was scanned in reverse" on if you flipped the stack, check the order preview, and click Mix PDF pages.

What happens if the two files have different page counts?

By default the leftover pages of the longer file are added at the end. You can turn that off to leave them out. If the counts differ by more than one, the tool warns you, because a double-sided scan should not.

Can I take more than one page from each file at a time?

Yes. Set how many pages to take from A and from B on each turn, for example 2 and 1 gives A1, A2, B1, A3, A4, B2.

Are my PDFs uploaded?

No. The pages are read and reordered in your browser with JavaScript, and the new PDF is created on your device. Nothing is sent to our server.

Does mixing reduce quality?

No. Pages are copied exactly as they are, without re-compressing images, so text stays selectable and scans keep their resolution.

Does it work with password-protected PDFs?

Not directly. Remove the password with Unlock PDF first, then mix the unlocked files.

Alternate & Mix PDF

Combine two PDFs by taking pages from each in turn - A1, B1, A2, B2 - instead of one file after the other. Made for single-sided scanners: scan the fronts, flip the stack, scan the backs, and get one document in reading order. Your files are processed in your browser and never uploaded.

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Will this put my pages in order?

Fronts and backs scanned as two PDFs

Reversed or in normal order, with equal page counts or one page apart.

One PDF with all fronts first, then all backs

Use "One file, fronts then backs".

Pages in some other order, or a few pages out of place

Drag pages into place by hand instead.

Organize PDF pages

Keeping bookmarks and fillable form fields

Bookmarks are not carried over and form fields may stop being editable. Flatten forms first if their values matter.

Flatten the PDF

Password-protected PDFs

Remove the password first, then mix.

Unlock PDF

Features

Alternates pages from two PDFs: A1, B1, A2, B2...
"Scanned in reverse" option for backs that come out last page first
Take several pages from each file per turn (e.g. 2 from A, 1 from B)
One-file mode for a scan with all fronts first, then all backs
Preview of the new page order before you mix
Pages are copied as they are: no re-compression, text stays selectable

When you need to interleave PDFs

Double-sided documents on a single-sided scanner

Scan the front sides, turn the stack over, scan the back sides, then mix the two files into one.

Question paper and answers

Put each answer page right after its question page.

Translations side by side

Alternate the original and translated pages so each pair can be read together.

How to put a double-sided scan back in order

Why the backs come out reversed

A scanner with a document feeder but no duplex scans one side of each sheet. After the fronts you turn the whole stack over, so the last sheet is now on top and its back is scanned first. That is why the "B was scanned in reverse" option is on by default: the tool takes file B from its last page to its first.

If your backs came out in normal order (for example you re-sorted the sheets by hand), turn the option off. The order preview shows exactly which page goes where, so check it before you mix.

Two files or one?

Two files: one PDF of front pages (A) and one of back pages (B). Use the swap button if you added them the wrong way round.
One file: some scanner apps save everything into a single PDF, all fronts first and then all backs. Choose "One file, fronts then backs" and the tool splits it in the middle (the extra page of an odd count is treated as a front).
The two files should differ by one page at most. A bigger gap usually means a page was missed or double-fed, and the tool warns you.

Related PDF tools

Want one whole file after another instead? Use Merge PDF.
To move, delete or rotate individual pages afterwards, use Organize PDF.
No scanner? Scan to PDF with your phone camera.
To pull the fronts and backs apart again, Split PDF by page range.