Double-Sided Scan Combiner Beta

Plenty of scanners promise double-sided scanning and then chew the paper the moment they try to flip it. The reliable workaround is to give up on the flip: scan the fronts of the whole stack in one pass, turn the stack over, scan the backs in a second pass, and put the two files back together afterwards. That is what this tool does.

The catch is the order. Turning the stack over feeds the last sheet first, so the backs arrive in reverse: the first page of your backs scan is the back of your last sheet. Combining the two files naively gives you a document where the second half is upside down in sequence. This tool reverses the backs by default and interleaves them with the fronts, so sheet one becomes pages one and two, sheet two becomes pages three and four, and so on. If your workflow restacks the paper instead of flipping it, one checkbox turns the reversal off.

Two things commonly go wrong beyond the ordering. An odd number of sheets means the final back is blank and often never gets scanned, leaving one more front than back; the tool reports that and pairs everything else correctly rather than shifting the whole document. And a stack of one-sided paper produces a backs scan that is entirely blank, which is why you can have those pages detected and dropped. Because a jam can also silently swallow a page mid batch, the preview pairs every front with its back so you can confirm the alignment before exporting anything, and any page can be opened full size and zoomed when the thumbnails are too small to read.

Everything happens in your browser using the open-source pdf-lib and pdf.js libraries. Your scans are never uploaded, which matters more than usual here, since the documents people scan in bulk tend to be contracts, tax records and medical paperwork.