Many home and office scanners, and most phone scanning apps, only scan one side of the paper at a time. You can still get a proper double-sided PDF, with every page in the right order, in two passes and one minute of tidying up.
1. Scan all the fronts
Put the whole stack in the feeder face up (or face down, as your scanner wants) and scan it into one PDF. Call it something like fronts.pdf. Don't take pages out or add any: the order matters later.
2. Turn the stack over and scan all the backs
Take the stack out of the tray exactly as it came out, turn it over in one go, and scan again into backs.pdf. Because you turned the whole stack, the backs come out in reverse: the back of the last sheet first. That's normal, and the next step fixes it.
3. Put the pages together
Open combine double-sided scans and choose both files. It takes front 1, back 1, front 2, back 2 and so on, and reverses the backs for you. The list of pages shows which sheet each one came from, so you can check before you download.
- Backs already in order? Some scanners and apps put them the right way round. Untick “Backs are in reverse order”.
- Everything in one PDF? If you scanned the fronts and then the backs into a single file, choose “One PDF: all fronts, then all backs” instead.
- Fronts and backs mixed up? Use “Swap fronts and backs”.
4. Remove the blank backs
Single-sided sheets in the stack leave empty pages. The remove blank pages tool finds them, including pages with only scanner shadows, and lets you keep any you want.
Tips for a clean scan
- Fan the stack and take out staples and paper clips before each pass, so pages don't feed two at a time.
- Count the pages: both files should have the same number of pages, one per sheet.
- Scanning at 200–300 DPI is enough for text. To make the PDF smaller afterwards, use compress PDF.