1. A document management apparatus for connection through a network to an image forming device, a document file server, and a workflow server, respectively, the document management apparatus comprising: an information acquisition unit configured to acquire, from the image forming device through the network, image data of a paper document including a signature block at a predetermined position of the paper document, and a user ID that identifies a user who requests the image forming device to read the image data from the paper document; an extraction unit configured to receive, from the document file server through the network, a document file which is acquired from a document file accumulation unit of the document file server in response to a document file ID that identifies the document file and is included in the image data of the paper document, and transmitted to the document management apparatus by the document file server, to extract revision data that is added to the paper document, based on difference data indicating differences obtained by matching of the image data of the paper document with image data of the document file, and to determine propriety of approval of the revision data based on an item of the extracted revision data corresponding to the predetermined position of the paper document; and a registration unit configured to transmit, to the workflow server through the network, a request of registration of approval information indicating the propriety of approval of the revision data, the request of registration including the approval information, the user ID and the document file ID, wherein the extraction unit is configured to request the document file server to register, into the document file accumulation unit, the document file, the revision data and the user ID that are associated with the document file, by using the document ID contained in the image data of the paper document, and wherein the workflow server is configured to register, in response to the request of registration received from the registration unit, state information indicating a progress of approval of the document file associated with the document ID.