# Merge Odd and Even Scanned Pages - Interleave Fronts & Backs

> Combine a fronts PDF and a backs PDF from a single-sided scanner into correct duplex order, with reversed backs, 180° rotation, blank padding and preview.

- URL: https://qilingtools.com/en/pdf/interleave
- Category: PDF Tools (https://qilingtools.com/en/pdf)
- Tags: [PDF](https://qilingtools.com/en/tags/pdf), [Merge & Split](https://qilingtools.com/en/tags/split-merge), [Scanning](https://qilingtools.com/en/tags/scan)
- Last updated: 2026-10-26
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

Most home and office scanners have a single-sided document feeder, so scanning a double-sided document means feeding the stack once for the fronts, flipping it and feeding it again for the backs. You end up with two files — pages 1, 3, 5… in one and …6, 4, 2 in the other, usually in reverse order. This tool interleaves them into a single PDF in the right order: front 1, back 1, front 2, back 2 and so on. Reversed backs are assumed by default (that’s what you get when you flip the whole stack), and you can switch it off. If the backs came out upside down because the stack was flipped top to bottom, tick Rotate backs 180° — only the page rotation is changed, so nothing is recompressed. When the counts differ, for example because the last sheet was one-sided, you can pad the missing backs with blank pages of the same size (handy for duplex printing later) or simply skip them. It also works with a single file whose first half is fronts and second half is backs, with an adjustable split point. Thumbnails show the final page order before you merge. Everything runs in your browser, so your scans are never uploaded.

## How to use

1. Upload two PDFs — the first with all fronts, the second with all backs (drag to swap) — or one PDF with fronts first and backs second
2. Check the reversed-backs, rotate-backs and unequal-count options and review the thumbnail page order
3. Click Merge fronts & backs and download the correctly ordered PDF

## Features

- Interleave a fronts file and a backs file
- Single-file mode with an adjustable split point
- Handles reverse-order backs
- Lossless 180° rotation of backs
- Blank-page padding or skipping when counts differ
- Thumbnail preview of the final order
- Original scan quality kept
- Runs locally, nothing uploaded

## FAQ

### How do I know whether the backs are in reverse order?

If you flipped the whole stack after scanning the fronts and fed it again, the first page scanned is the back of the last sheet, so the backs file is reversed — keep the default. If you turned each sheet over in its original order, or your scanning software already reversed them, untick the option. In the thumbnails, front 1 should be followed by the back of sheet 1.

### The backs are upside down — what can I do?

That happens when the stack is flipped along its long edge top to bottom. Tick Rotate backs 180° to fix it. Only the page’s rotation setting changes, so image quality and file size stay the same.

### What if there are more fronts than backs, or vice versa?

Usually the last sheet was one-sided and the scanner skipped its blank back. Backs are paired with sheets starting from sheet 1; sheets without a back can get a blank page of the same size, which keeps duplex printing aligned, or be left as is. Any extra pages go to the end, and the preview labels where every page comes from.

### Are my files uploaded?

No. Reading, reordering and saving all happen in your browser, which makes it safe for contracts, IDs, medical records and other sensitive scans.

## Related tools

- [Merge PDF](https://qilingtools.com/en/pdf/merge): Free online PDF merger: combine several PDF files into one in the order you choose, with reordering. Processed locally in your browser, no upload, no sign-up.
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