There are two techniques, depending on if your scanner has a document feeder supporting duplex scanning.
Check to see if “Input | Mode” has “Duplex Feeder” as an option. This will do two-sided scanning.
If not, then try the following:
- Scan the front sides of a document to a multi-page PDF file
- Scan the back sides of a document to the same multi-page PDF file
- Click on the thumbnails with the right mouse button and choose “Interleave”
Note that you need exactly the same number of front sides and back sides - there has to be an even number of pages in the multi-page PDF file.