A — front sides (pages 1, 3, 5 …)
Click to upload or drop a PDF
Or the first of any two PDFsB — back sides (pages 2, 4, 6 …)
Click to upload or drop a PDF
Or the second PDFAbout interleaving PDF pages
Many home and office scanners scan one side only. To scan double-sided papers, you scan the stack once for the front sides, turn it over, and scan it again for the back sides. Now you have two PDFs — or one PDF with all the fronts first — and the pages are in the wrong order.
This tool interleaves them: page 1 from the fronts, page 2 from the backs, page 3 from the fronts, and so on. Because the back sides usually come out last page first, it reverses them for you.
It also works for any two PDFs whose pages should alternate, for example a text in two languages. The pages are copied as they are, with no loss of quality, and nothing is uploaded.
Features
- Fronts + backs → one PDF — in the right page order
- Reversed backs — on by default, because a turned-over stack scans last page first
- Two PDFs or one — also for one scan that holds all the fronts first, then all the backs
- Alternate any two PDFs — one page at a time, or 2, 3 or 4 pages at a time
- Order preview — see where every page comes from before you download
- Warning when counts differ — leftover pages go at the end
- No quality loss — pages are copied, not redrawn
How it puts the pages in order
Say you scan 3 double-sided sheets. The first scan gives the fronts: A1, A2, A3. You turn the stack over and scan again. The scanner now starts with the back of the last sheet, so the second PDF is B1 = back of sheet 3, B2 = back of sheet 2, B3 = back of sheet 1.
| New page | Comes from | Which side |
|---|---|---|
| 1 | A1 | front of sheet 1 |
| 2 | B3 | back of sheet 1 |
| 3 | A2 | front of sheet 2 |
| 4 | B2 | back of sheet 2 |
| 5 | A3 | front of sheet 3 |
| 6 | B1 | back of sheet 3 |
So the order is A1 B3 A2 B2 A3 B1. If your scanner keeps the back sides in the normal order (some feeders do), untick reverse order and you get A1 B1 A2 B2 A3 B3.
One PDF with fronts first
Some scanner apps put both passes into one file: first all the fronts, then all the backs. Choose One PDF. With 10 pages, pages 1–5 are the fronts and pages 6–10 the backs; with the backs reversed, the new order is 1, 10, 2, 9, 3, 8, 4, 7, 5, 6.
If the file has an odd number of pages, the first half rounded up is taken as the fronts, and the page shows a note.
Alternating any two PDFs
Untick reverse order, and A and B simply take turns: A1, B1, A2, B2 … With Pages at a time set to 2, two pages come from each file in turn: A1, A2, B1, B2, A3, A4 … That is useful for:
- A text and its translation, page by page
- Questions and answer sheets
- Slides and the notes that go with them
When the page counts differ
When one file has more pages, the extra pages go at the end, and a warning shows. A common case: the last sheet had an empty back, and the scanner skipped empty pages. With reversed backs the order is then still right, because the missing page is the one that would have come last.
Common uses
- Double-sided letters and contracts on a scanner with a one-sided feeder
- School papers and forms printed on both sides
- Old books and notebooks scanned in two passes
- Two language versions of a document, page by page
- Front and back of ID cards or receipts scanned as two batches
Good to know
- The pages are copied as they are: scans keep their quality, text stays text
- A password-protected PDF must be unlocked first with Unlock PDF
- Pages scanned upside down can be turned afterwards with Rotate PDF
- Your choice of reverse order and pages at a time is remembered in this browser
Frequently asked questions
How do I merge odd and even pages into one PDF?
Upload the PDF with the odd pages (the fronts) as A and the PDF with the even pages (the backs) as B. Leave reverse order ticked if you turned the stack over to scan the backs. Check the order preview and click Download PDF.
Why are the back pages in reverse order?
When you turn the stack over, the last sheet is now on top, so the scanner reads its back first. The second PDF starts with the back of the last sheet and ends with the back of the first sheet. The tool reverses it so that each back follows its own front.
How do I scan double-sided pages with a one-sided scanner?
Scan the stack once and save the fronts as a PDF. Turn the whole stack over without changing the order, scan it again and save the backs as a second PDF. Then put both PDFs here.
What if the two PDFs have a different number of pages?
The pages are paired as far as they go, and the pages left over are added at the end. A warning tells you. Check the order preview, and use Organize PDF afterwards if a page needs to move.
Can I use this to merge two PDFs page by page?
Yes. Untick reverse order. Then the pages simply alternate: A1, B1, A2, B2 … Choose 2, 3 or 4 pages at a time to take more pages from each file in turn.
Are my files uploaded?
No. Both PDFs are read and the new one is made inside your browser. Nothing is sent to a server.
Related tools
- Merge PDF — join PDFs one after the other instead of page by page
- Scan to PDF — scan both sides of your papers with a phone camera
- Organize PDF — move a page that is still in the wrong place
- Delete PDF Pages — remove empty back sides after scanning
- Split PDF — take the result apart into separate documents
- Rotate PDF — turn pages that were scanned upside down
How to use it
- Choose Two PDFs (fronts and backs) or One PDF (all fronts, then all backs)
- Upload the front sides as A and the back sides as B
- Keep reverse order ticked if you turned the stack over to scan the backs
- Check the new page order and the small previews
- Click Download PDF
