A document feeder is part of a fax machine or multifunction printer/scanner/copier/fax that takes the pages to faxed, scanned, or copied.
Document feeders are an alternative to “scanning off the glass” (the act of scanning or copying a document on the flatbed glass of the machine). They are preferred by many users because they are very good at inputting many pages.
The two types of document feeders. Regular document feeders only read one side of pages, while RADF (reversing automatic document feeders) can scan both sides of pages.