According to an aspect of the invention, a document management system includes a document state storage unit, a manipulation control unit, a stamp image storage unit, and a state change unit. The document state storage unit stores document state information representing states concerning document validity of electronic documents stored in a document storage unit. The manipulation control unit refuses a request from a user for manipulating one of the electronic documents when the document state information corresponding to the one of the electronic documents indicates that the one of the electronic documents is invalid at present. The stamp image storage unit stores a plurality of stamp images each corresponding to any one of possible states represented by the document state information.