1. A document management apparatus including one or more programs of instructions which are stored in a non-transitory storage medium and are executable by a processor of a host computer to configure the host computer to comprise: a comments extraction module to compare (a) a source document registered in a document repository and (b) a scan document image of the source document, to extract, from the scan document image, comments added to the source document by a comments author and determine a position of the comments in the document image; a registration module to register the extracted comments and corresponding position, as comments content in association with the source document in the document repository, the comments content being registered in association with a user name of the comments author of the registered comments; and a contents review module to provide, upon request from a user terminal, the comments content along with the user name of the author in a first interface of a document review user interface on the user terminal, wherein when the registered comments content includes plural sets of comments and corresponding user names of the respective authors of the registered sets of comments, a second interface of the document review user interface displays, for user selection, each of the plural registered sets of comments along with the respective registered user names which are registered in association with the source document in the document repository, and displays, upon receiving the user-selection of one or more of the registered sets of comments through the second interface of the document review user interface, the user-selected sets of comments superposed on an image of the source document in the first interface of the document review user interface on the user terminal.