1. A document conversion apparatus for converting document image data to an electronic document, said document conversion apparatus comprising: a memory that stores program instructions to perform a document conversion function; and a processor that executes the program instructions stored in the memory to perform the document conversion function; wherein the processor executes the program instructions as functional sections, the functional sections including: a character region extraction section that extracts character regions from the document image data, a table of contents data generation section that generates table of contents data based on the extracted character regions and page numbers of the character regions, an electronic document generation section that generates the electronic document having a table of contents based on the document image data and the generated table of contents data, a character recognition section that performs character recognition on the extracted character regions, a keyword extraction section that extracts keywords from a result of the character recognition, and an index data generation section that generates index data based on the extracted keywords and page numbers thereof, wherein said table of contents data generation section comprises a table of contents link information adding section that adds link information to respective ones of items in the generated table of contents data for linking the items in the generated table of contents data with corresponding positions in the electronic document in which the items are described, wherein said index data generation section comprises an index link information adding section that adds links information to respective ones of items in the index data for linking the items in the generated index data with corresponding positions in the electronic document in which these items are described, and wherein said electronic document generation section generates the electronic document having the table of contents and an index based on the document image data, the table of contents data, and the index data.
1. A document conversion apparatus for converting document image data to an electronic document, said document conversion apparatus comprising: a memory that stores program instructions to perform a document conversion function; and a processor that executes the program instructions stored in the memory to perform the document conversion function; wherein the processor executes the program instructions as functional sections, the functional sections including: a character region extraction section that extracts character regions from the document image data, a table of contents data generation section that generates table of contents data based on the extracted character regions and page numbers of the character regions, an electronic document generation section that generates the electronic document having a table of contents based on the document image data and the generated table of contents data, a character recognition section that performs character recognition on the extracted character regions, a keyword extraction section that extracts keywords from a result of the character recognition, and an index data generation section that generates index data based on the extracted keywords and page numbers thereof, wherein said table of contents data generation section comprises a table of contents link information adding section that adds link information to respective ones of items in the generated table of contents data for linking the items in the generated table of contents data with corresponding positions in the electronic document in which the items are described, wherein said index data generation section comprises an index link information adding section that adds links information to respective ones of items in the index data for linking the items in the generated index data with corresponding positions in the electronic document in which these items are described, and wherein said electronic document generation section generates the electronic document having the table of contents and an index based on the document image data, the table of contents data, and the index data. 6. The document conversion apparatus according to claim 1 , wherein the functional sections further comprise: a reliability determination section that determines a reliability of a result of the character recognition, and wherein said table of contents data generation section generates the table of contents data in which partial character image data for a title portion is made displayable and character codes resulting from the character recognition on the title portion are made undisplayable when the reliability is below a threshold value, and generates the table of contents data in which fonts corresponding to the character codes are made displayable when the reliability is above the threshold value.