6. An apparatus configured to display digital document data with partial text data therein replaced with mask data, the apparatus comprising: a processor; and a non-transitory computer readable storage medium comprising modules executable by the processor, wherein the non-transitory computer readable storage medium comprises: a data acquisition module configured to acquire the digital document data; a designation acceptance module configured to accept designation of an instance of the partial text data to be replaced, the partial text data located within the digital document data; a replaced document data generating module configured to generate replacement document data that comprises a copy of the digital document data in which the instance of the partial text data is replaced with an identification information corresponding to said instance of the partial text data; a replaced document data storage unit configured to store a replaced document data, which comprises the replacement document data and an identification of a region of the replacement document data that includes the identification information corresponding to the instance of the partial text data, wherein the replacement document data comprises more than one region; a selection acceptance module configured to accept selection of a rule information piece from a plurality of rule information pieces, which comprises a replacement information that associates the identification information with a mask pattern, the rule information piece corresponding to said instance of the partial text data; and a replacing module configured to replace, based on the replacement information, the identification information of the instance of the partial text data included in the replaced document data with the mask pattern.
6. An apparatus configured to display digital document data with partial text data therein replaced with mask data, the apparatus comprising: a processor; and a non-transitory computer readable storage medium comprising modules executable by the processor, wherein the non-transitory computer readable storage medium comprises: a data acquisition module configured to acquire the digital document data; a designation acceptance module configured to accept designation of an instance of the partial text data to be replaced, the partial text data located within the digital document data; a replaced document data generating module configured to generate replacement document data that comprises a copy of the digital document data in which the instance of the partial text data is replaced with an identification information corresponding to said instance of the partial text data; a replaced document data storage unit configured to store a replaced document data, which comprises the replacement document data and an identification of a region of the replacement document data that includes the identification information corresponding to the instance of the partial text data, wherein the replacement document data comprises more than one region; a selection acceptance module configured to accept selection of a rule information piece from a plurality of rule information pieces, which comprises a replacement information that associates the identification information with a mask pattern, the rule information piece corresponding to said instance of the partial text data; and a replacing module configured to replace, based on the replacement information, the identification information of the instance of the partial text data included in the replaced document data with the mask pattern. 8. The apparatus according to claim 6 , wherein the non-transitory computer readable storage medium further comprises: a cancellation request acceptance module configured to accept an application cancellation request for one of the plurality of rule information pieces; and a re-replacing module configured to replace identification information included in the replaced document data with one of the mask data or the partial text data for all of the plurality of rule information pieces, except for the one of the plurality of rule information pieces that has been canceled, responsive to accepting the application cancellation request.