Sejda PDF

Alternate & mix PDF

Interleave pages from two documents into one file.

Drag & drop your files here

Supported: PDF

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About Alternate & mix PDF

Perfect for scanners that only handle one side of the paper: feed in the odd pages and the even pages and get a correctly collated document back, with the option to reverse either stack.

  • Fixes single-sided scanner output
  • Reverse either document
  • Works with uneven page counts

How to alternate & mix pdf

  1. 1

    Add both scans

    One file with the fronts, one with the backs.

  2. 2

    Reverse if needed

    Flip the second stack when it was scanned bottom-up.

  3. 3

    Mix the pages

    Pages alternate one by one into a single document.

A practical guide to alternate & mix pdf

Rescuing a document from a single-sided scanner

The classic scenario is a duplex contract run through a feeder that only reads one side. You end up with two PDFs: one holding every odd page, one holding every even page, often reversed. Load the odd file first, the even file second, enable reverse on the even stack, and mix. The result is a single document that reads one, two, three, four straight through. Before trusting a large batch, run a short test with the first few sheets so you can confirm the reverse setting is correct; getting that switch right on a small sample saves redoing a hundred-page job.

Handling stacks that do not match

Real scans are rarely perfectly even. If one file has more pages than the other, the extra pages are not lost; they are appended at the end in their original order once the alternation runs out. That behavior is handy when the last sheet of a document was single-sided and left a lonely front with no matching back. Still, it pays to check the page counts before mixing, because a large mismatch often signals a jam or a double-fed sheet during scanning. When the counts are wildly off, rescanning the shorter stack usually beats stitching around the gap afterward.

Finishing the reassembled file

Once the pages are interleaved correctly, a scan-based document usually benefits from a couple of follow-up steps. If some pages went through the feeder crooked, the deskew tool straightens them, and running OCR afterward makes the reassembled file searchable and ready to archive. If the mix left the document in near-perfect shape but one or two pages are still rotated, jump into the organize tool for quick per-page fixes rather than remixing. Treat alternate and mix as the collation step, then polish appearance and text separately for the cleanest final document.

Frequently asked questions

Why do my double-sided scans come out in the wrong order?
Single-sided document feeders scan all the fronts in one pass, then all the backs, and the back stack is usually in reverse order because the sheets flip over. Alternate and mix interleaves the two files so page one, page two, page three fall back into place, and the reverse option corrects that flipped back stack.
Do I have to scan the backs upside down for this to work?
No. Scan both stacks the normal way. If the backs ended up reversed, just enable the reverse option on that second file before mixing, and the tool walks through it from the last page to the first so everything lines up.
Can I use this to combine a cover and body that alternate in a fixed pattern?
Yes. Beyond simple front-and-back collation, the adjustable step lets you pull a set number of pages from each file in turn, which suits repeating layouts like a certificate followed by its two-page appendix. Set the step to match your pattern before mixing.
Is this different from just merging the two files?
Very. Merge places one whole file after another, so all the fronts would still sit before all the backs. Alternate and mix weaves the pages together one at a time, which is exactly what reassembling a double-sided document needs.

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