Alternate and Mix PDF Pages
Alternate and mix PDF pages from two or more files: the first page of each, then the second, and so on. The classic use: a scanner that did all the fronts, then all the backs.
Alternate & Mix PDFs
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Settings appear once you add a PDF.
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Every request this page makes is listed as it happens. You’ll see our own code loading, and for some formats a codec engine, but never your file going out.
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Check it yourself: open your browser’s developer tools on the Network tab, or turn off Wi-Fi once the page has loaded. The tools keep working.
- 100% private Your PDFs never leave this device. Everything runs in your browser.
- No limits No file-size cap, no watermark, no sign-up and no daily quota. Free.
- Batch ready Add as many PDFs as you like; each one is handled and saved in one go.
How to alternate and mix PDF pages
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Add your PDFs: Drop the PDFs — fronts first, then backs. Use the arrows to set which file comes first.
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Check the settings: If the backs were scanned by turning the whole stack over, switch on Reverse the last file’s pages.
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Save the result: Mix. You get one PDF: front 1, back 1, front 2, back 2… When one file runs out, the rest of the other follows.
Why it doesn’t upload
Double-sided scans are usually paperwork — contracts, forms, medical records. Putting them back together here means both halves stay on your device.
Check it in your browser’s Network tabWorth knowing
- Pages are copied exactly; nothing is re-scanned or recompressed.
- If the files have different page counts, the leftover pages go at the end in order.
- Password-protected PDFs need their password removed first.
Under the hood
What happens to your file
Pages from two or more files are interleaved — A1, B1, A2, B2 — with any source reversed first, which is how a stack scanned fronts then backs becomes one document in order. Pages are copied as they are; nothing is re-scanned or recompressed.
Reference: pdf-lib documentation
Why interleave PDF pages automatically?
Scanners without double-sided feeding make you scan a stack twice: all the fronts, then all the backs. You end up with two PDFs that need weaving together page by page — front 1, back 1, front 2, back 2. Doing that by hand on a 40-page document is tedious and easy to get wrong.
This tool does it in one go, in your browser, copying every page exactly. Turn on reverse for a backs-file that was scanned last-page-first, which is how most stacks come out after flipping.
Common uses for alternating and mixing PDF pages
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Double-sided documents on a single-sided scanner
Combine the fronts PDF and the backs PDF into one correctly ordered file.
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Bilingual documents
Alternate pages from an English and a translated version for side-by-side reading.
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Questions and answers
Interleave a worksheet with its answer sheet, page by page.
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Before-and-after comparisons
Alternate pages of two drafts to review them in sequence.
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Slides with notes pages
Mix exported slides with a notes PDF, a set of pages at a time.
Tips for combining front and back scans
- Flipped the stack to scan the backs? Turn on Reverse the last file’s pages — the backs came out in reverse order.
- Put the fronts file first in the list; the result starts with the first file’s first page.
- Use Pages at a time to take two or more pages from each file per turn.
- If the files have different page counts, the extra pages go at the end in order.
- Just need everything one file after another? That’s an ordinary merge.
Questions
How do I combine front and back scans into one PDF?
Add the fronts PDF, then the backs PDF, and press Mix pages. If the backs are in reverse order — common when you flip the stack — switch on Reverse the last file’s pages first.
What does interleaving PDF pages mean?
Taking pages alternately from two or more documents: the first page of each, then the second of each, and so on, into one file.
Can I merge odd and even pages?
Yes — that’s the same job. Put the odd pages first and the even pages second.
Can I take two pages at a time from each file?
Yes, under Advanced: set how many pages to take from each file before switching.