1. A document processing device for processing image data, comprising: a medium identification information acquiring unit configured to acquire medium identification information from an image of the medium identification information included in the image data; a process information acquiring unit configured to acquire, based on the medium identification information, process information pertaining to a currently-executing process in a currently-executing workflow associated with the medium identification information; a form definition information acquiring unit configured to acquire, based on the process information pertaining to the currently-executing process, form definition information of a form corresponding to the currently-executing process; and a region image acquiring unit configured to acquire, based on the form definition information, a region image of a predetermined region in the image data, which predetermined region corresponds to an entry region in the form where written-input information is written in at the currently-executing process.