Which type of scanner uses a flat surface for scanning documents?

A flatbed scanner is specifically designed to use a flat surface for scanning documents. This type of scanner typically features a glass plate where documents are placed for scanning. The scanning apparatus moves beneath the glass, capturing the image of the document. Flatbed scanners are ideal for a variety of document types, including books and fragile items, as they do not require the physical insertion of the items into a feed mechanism, which can sometimes cause damage.

While other scanners may have different designs and functionalities, they do not focus on the flat surface scanning method. For instance, document scanners and multi-function scanners can perform various tasks, but they often incorporate a feed mechanism rather than requiring a flatbed surface. Portable scanners are designed for on-the-go scanning and may also lack the flatbed feature. Hence, the flatbed scanner stands out as the correct answer when identifying a scanning device that utilizes a flat surface.