Alternate & Mix PDF

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.