1. A document processing device comprising: a document data acquiring part for acquiring document data; a character string extracting part for extracting character strings satisfying a predetermined condition for character string extraction from said document data acquired by said document data acquiring part; a format creating part for deriving the respective features of said character strings extracted by said character string extracting part, and creating a format containing the derived features in the form of data; a display part on which said character strings extracted by said character string extracting part are displayed in a list form, and on which the format created by said format creating part is displayed; and a format correcting part for correcting the format, wherein said character string extracting part extracts character strings again to conform to the format corrected by said format correcting part.