Alternate & Mix PDF
Takes two PDF files and alternates their pages into one document — a page from the first file, then a page from the second, and so on. Especially useful for reassembling a document scanned on a single-sided scanner in two passes (fronts in one file, backs in another), with an option to automatically reverse the second file's order for the common case where the back pages were scanned by re-feeding the same flipped stack — entirely in your browser, with no file ever uploaded to a server.
Both of your files are processed entirely on your device and are never uploaded to our servers.
Especially useful for reassembling pages scanned on a single-sided scanner in two passes (fronts in one file, backs in another) into one correctly-ordered document.
First file (front pages)
Drag a PDF file or choose one
Second file (back pages)
Drag a PDF file or choose one
What this tool does
Interleaves two PDFs — a page from the first, then a page from the second, and so on. It includes an option to reverse the second file, which exists specifically to solve double-sided scanning on a scanner that cannot do it.
When to use it
- You scanned the fronts into one file and the backs into another and need them merged in the right order.
- You have one file of odd pages and another of even pages and want a complete document.
- You want two versions of a document interleaved for page-by-page comparison.
How to use it
- Put the first document in the first file slot.
- Put the second document in the second file slot.
- Turn on the reverse option if the backs were scanned by flipping the whole stack, which reads them in the opposite order.
- Run the mix to download the interleaved file.
A practical example
Input
A "fronts" file containing pages 1, 3, 5 and a "backs" file that came out as 6, 4, 2 because the stack was flipped — so you turn the reverse option on.
Output
A 6-page PDF in the correct 1, 2, 3, 4, 5, 6 order.
Without the reverse option you would get 1, 6, 3, 4, 5, 2 — the exact mistake the option exists to prevent.
Limitations
- Only two files can be mixed at a time.
- If the two files have different page counts, the leftover pages are appended at the end rather than dropped.
- The alternation is strictly one page at a time; interleaving in groups (two-and-two, say) is not offered.
Privacy and processing
Both files are processed entirely on your device and neither is uploaded to our servers.
Technical notes
- The page-ordering logic is a pure function independent of pdf-lib and the browser, with its own unit tests — because it is the part most prone to an off-by-one error.
Frequently Asked Questions
The tool alternates between the two files until the shorter one runs out, then appends the remaining pages from the longer file at the end, in their original order.