Alternate and mix pages from two PDFs

You scanned the fronts of a stack of paper, turned the stack over, scanned the backs, and now you have two PDFs where you wanted one. This takes a page from each file in turn — front 1, back 1, front 2, back 2 — and writes them into a single document. If you flipped the whole pile in one go, the backs are in reverse order, and one tick puts them right.

It does not notice blank backs. A scanner that produced an empty page for every unprinted side will have those interleaved too; delete pages with ‘even’ takes them out afterwards.

Mix two PDFs

No account. Your upload is deleted after 2 hours, the result after 24 hours.

How it works

  1. Add the fronts first, then the backs. Order matters: the first file gives page 1, the second gives page 2. Up to ten files can take part, and each one contributes a page per round.
  2. Say whether the backs are reversed. Turning a whole pile over puts its last sheet on top, so the backs come out last-to-first. Tick the box when that is what happened, and leave it alone if you re-fed the sheets one at a time.
  3. Read the first four pages. Open the result. If pages 1 to 4 run front 1, back 1, front 2, back 2, the whole document is right. If pages 2 and 4 have swapped places, run it again with the reverse box the other way.

What the options do

The form above lists the options this tool is running today, straight from the server. This is what they are for.

The second file is back to front
Reads the second file from its last page backwards. This is the setting that matters. A scanner that takes the pile face-up gives you fronts 1 to n; turn that pile over and the backs come out n to 1, so without this tick every sheet gets somebody else’s back. It applies only to the second file — if you are mixing three or more, put the reversed one second.
Start shorter files again when they run out
A file that runs out begins again at its first page instead of dropping out. That is for the case where one file is a single sheet that belongs behind every page of the other: a terms page, a letterhead, a continuation notice. Leave it off for a front-and-back scan, where two files of different lengths usually means a sheet was double-fed — the result tells you the two lengths either way.

What this tool does not do

  • It does not notice blank backs. A scanner that produced an empty page for every unprinted side will have those interleaved too; delete pages with ‘even’ takes them out afterwards.
  • Only the second file can be read in reverse. With three or more files, the reversed one has to be second.
  • Pages are copied, not redrawn, so nothing is straightened, cleaned up or resized. Deskew is the tool for a scan that came in at an angle.
  • The result is a new document: the sources’ bookmarks and form definitions are left behind, though each page keeps its own annotations.
  • It cannot work out for itself which file is which. Fronts first, backs second, every time.

What happens to your file

The file is uploaded because Alternate & Mix PDF runs on our server rather than in the browser tab. It is kept for at most 2 hours and the result you download for 24 hours, then a scheduled job deletes both — a job has to be able to read the file while it runs, and you have to be able to retry a failed conversion without re-uploading. Neither needs longer.

Nothing about the contents is logged, and no one reads your documents. The retention page lists the same numbers the code enforces, and the privacy policy says who can reach the storage they sit in.

Questions

My scanner made two files, fronts and backs. Which one goes first?
The fronts. The first file contributes page 1, the second contributes page 2, and so on down the pile. If the backs were scanned by turning the whole stack over, tick ‘the second file is back to front’ as well.
What if one file has more pages than the other?
The longer file carries on alone once the shorter one runs out, and the result tells you both lengths. On a front-and-back scan that nearly always means a sheet was double-fed — worth checking before the paper goes in the bin.
Can I mix more than two files?
Yes, up to ten. Each round takes one page from each file in the order you listed them. Only the second file can be read in reverse, so if one of them is a flipped pile, put it second.
How do I get rid of the blank backs?
Mix the files first, then run delete pages with ‘even’ to drop every second page. If only some backs were blank, list those page numbers instead. Doing it in that order keeps the numbering easy to follow.
Can I put the same terms page behind every sheet?
Yes. Upload the multi-page document first and the single terms page second, and turn on ‘start shorter files again when they run out’. The terms page is then repeated after every page of the first file.