9. The apparatus according to claim 7 , further comprising: a position information extraction unit to extract position information regarding each symbol in the text area, wherein the key index generation unit arranges the one group of symbols based on the extracted position information regarding each symbol.
7. A document processing apparatus, comprising: a symbol-related information acquirement unit to identify a text area from a scanned document, extract symbols from the identified text area, and acquire symbol-related information regarding each extracted symbol; a symbol division unit to divide the extracted symbols into a plurality of groups based on a preset reference value regarding the symbol-related information; and a key index generation unit to generate a key index by arranging one group of symbols from among the divided groups, wherein the symbol-related information is information regarding at least one of height, width, and stroke width of the corresponding extracted symbol.