Alternate & mix
Interleave two files, reversing the second - the double-sided scan fix.
This tool runs entirely in your browser. Your file is never uploaded, and you can verify that in your browser's network tab. Verify it yourself: open your browser's network tab and watch. You will see one small request asking whether you have tasks left - a tool name and a hash, never the file.
What this does
This weaves two documents together one page at a time, reversing the second as it goes. It exists to solve one specific and very common problem, and it solves it in a single pass.
You have a double-sided stack of paper and a scanner that only scans one side. So you scan the stack once to get all the fronts, flip the whole stack over, and scan it again to get all the backs - but because you flipped the stack, the backs come out in reverse order. Front page one belongs with back page last. This tool puts them together correctly.
How it works
- Scan the stack face-up to get the fronts, then flip the whole stack and scan again to get the backs.
- Drop both PDFs onto this page. The first file in the list is the fronts.
- Leave reverse the second file on - that is what corrects the flipped stack.
- Press Mix files.
- The download starts on its own. Check a few pages before throwing the originals away.
Reversing the second file is on by default because that is what the flipped-stack workflow needs. If your two files are already both in forward order - for instance you scanned odds and evens separately in the same direction - turn it off and you get a plain interleave instead.
The two files do not have to be the same length. If a page jammed and one file is short, the remaining pages of the longer file are appended in order rather than dropped, so nothing goes missing while you work out which sheet went astray.
Pages per turn handles booklet scans. Scanning folded sheets gives you two pages of content per scanned side, so setting the value to two takes two pages from each file in turn instead of one.
This tool interleaves at the page level, which means it cannot share resources between the two documents the way a straight merge can. A pair of scans with an identical letterhead will produce a slightly larger file than merging them would. Run Compress PDF afterwards if that matters.
What this tool cannot do
- Because pages are interleaved one at a time, shared resources are stored more than once and the result can be larger than a plain merge.
Questions people ask
- Why would I need this instead of merging?
- Merging puts one document after the other: all the fronts, then all the backs. What you need for a double-sided scan is front 1, back 1, front 2, back 2 - and with the backs in reverse order, because flipping the stack reversed them. That is what this tool does and merging cannot.
- My two files have different page counts. Will it still work?
- Yes. Pages are interleaved for as long as both files have pages, then whatever remains in the longer file is appended in order. Nothing is discarded, so you can see what went wrong.
- When should I turn off reverse the second file?
- When both files are already in forward order - for example if your scanner produced separate odd-page and even-page files in the same direction, or if you re-sorted the stack before the second scan instead of flipping it.
- What is pages per turn for?
- Scanning folded sheets captures two pages of content on each scanned side. Setting pages per turn to two takes two pages from each file before switching, which reassembles that kind of scan correctly.