Merge Double-Sided Scans

Merge Double-Sided Scans fixes the classic problem with a single-sided document feeder. You scan a stack of double-sided pages, flip it over and scan again, and end up with two PDFs: one holding pages 1, 3, 5 and one holding the backs, usually in reverse order because the last sheet came out on top. This tool weaves the two back together so the finished PDF reads front, back, front, back, exactly like the paper.

It suits anyone digitising paperwork at home or in an office: contracts, school reports, bank statements, signed forms or old letters. If your scanner saved everything into one file (all the fronts, then all the backs), switch to the one-file mode and tell it where the fronts end.

Before anything is saved you see every page as a thumbnail, labelled “Sheet 1 · Front”, “Sheet 1 · Back” and so on, so a wrong order is obvious at a glance. The work happens in your browser: the PDFs are not uploaded, there is no account and no watermark, and pages are copied as they are, without re-compressing your scans.

1. Choose how your scan was saved: “Two files: fronts + backs” or “One file: all fronts, then all backs”.
2. Add the fronts PDF in box 1 and the backs PDF in box 2 (or your single scan). Got them the wrong way round? Press the swap button between the boxes.
3. Leave “Backs are in reverse order” ticked for a normal sheet feeder; untick it if your backs already run 2, 4, 6. Tick “Leave out blank backs” to drop empty sides.
4. Check the preview: every page is labelled with its sheet and side. In one-file mode, adjust “Fronts end after page” if the split is off.
5. Press “Merge into one PDF”, then “Download PDF”.

• Two modes: separate fronts and backs files, or one file with all fronts followed by all backs (you set where the fronts end).
• Backs reversed by default, matching how sheet feeders scan the second pass, with a switch to turn it off.
• Swap button for when the fronts and backs files went in the wrong boxes.
• Different page counts are allowed: pages are paired in order and the extras go at the end, with a clear warning.
• Optional blank-back removal: each back is checked for ink, ignoring the grey edge scanners leave, and dropped pages stay visible, greyed out, in the preview.
• Thumbnail preview of the final order, labelled by sheet and side, before you save.
• Pages are copied as they are, so scans keep their full quality and the file size barely changes.
• Works on password-free PDFs from any scanner, phone scanning app or copier.

• If page 2 shows the back of the last sheet, your backs are in reverse order: tick “Backs are in reverse order”. If it shows the right page already, untick it.
• Blank detection looks for ink. Very faint pencil or a page with only a tiny page number can count as blank, so glance at the greyed-out tiles before saving.
• Pages scanned upside down stay upside down here. After merging, use Rotate PDF on just those pages.
• For a searchable document, run the merged file through PDF OCR afterwards; it is easier once the pages are in reading order.