1. A document management apparatus that manages a version of a binder document formed by integrating a plurality of original documents, the document management apparatus comprising: a first determination unit configured to, when updating a binder document, determine whether there is a same original document as the original document included in a new version of the updated binder document, in the original documents included in a past version of the updated binder document; and a storage unit configured to, when the first determination unit determines that there is the same original document in the original documents included in the binder document of the past version, store reference information regarding the same document as information corresponding to the original document included in the binder document of the new version and, when the first determination unit determines that there is not the same original document in the original documents included in the binder document of the past version, store an entity file of the original document as the information corresponding to the original document included in the binder document of the new version, wherein the reference information has a file size smaller than that of the entity file.