13. The document processing method according to claim 12 , further comprising: displaying the electronic document; and controlling a process of displaying to display the modification at the second position distinguishably.
12. A document processing method comprising: attaching a comment to an electronic document as additional information at a first position in a body of the electronic document; modifying the electronic document to include a modification at a second position in the body of the electronic document; determining, in response to a user's input indicating that the modification has been made by the user based on a content of the comment, that the electronic document is modified by the user accessing the electronic document to include the modification based on the content of the comment; associating the comment with modified place information indicating the second position at which the electronic document is modified, a character string at the second position prior to the modification, and a character string at the second position after the modification in response to determining that the electronic document is modified based on the content of the comment; and storing the associated information in a database.