PDF Interleave
Merge odd and even scans into reading order โ the duplex-scan fix.
About this tool
Two drop zones: the file with the odd pages (1, 3, 5โฆ) and the file with the evens. One click zips them together into reading order โ with a toggle for the even file being reversed, which is what a flatbed scanner naturally produces. On-device, lossless, free forever.
The duplex-scan problem, explained
Scanning a double-sided stack on a scanner without a duplex feeder goes like this: feed the stack (capturing pages 1, 3, 5โฆ), flip the whole pile over, feed it again โ and the second pass comes out BACKWARDS (โฆ6, 4, 2), because flipping a stack reverses it. The result is two PDFs that between them hold the document, in an order no reader wants. Interleaving with the reverse toggle on is the exact inverse of that ritual: odd 1, even n, odd 2โฆ reassembles reading order perfectly. A page-count mismatch bigger than one is the tool's polite warning that a sheet double-fed or a blank back was skipped โ recount before merging. Simple end-to-end joining is the merge tool; when the result needs hand-fixing, the organizer shows every page as a thumbnail; and a stack scanned bottom-up entirely is one click elsewhere.
Frequently asked questions
When do I leave 'reversed' on?
For the standard flatbed routine โ scan, flip the stack, scan again โ the second file comes out backwards, so leave it on. Turn it off only if your scanner app already re-sorted the second pass.
Why do my two files have different page counts?
They can legitimately differ by one (odd total). More than that usually means a double-feed or a skipped blank back โ worth checking before you merge.
Does interleaving touch page quality?
No โ pages are copied into the new file untouched. It's pure rearrangement.
Can I interleave more than two files?
This tool alternates exactly two, which covers the scanning ritual it exists for. For anything fancier, merge first and rearrange in the organizer.