1. A document management system that manages the storage and classification of documents and distributes information associated with the documents to a user, the system comprising: a storage unit that stores documents to construct a database; and a document processing unit that provides a user with a newly received information service application form that includes a service type section for setting a type of a newly received information service and an informing condition section for detecting a user-concerning document; receives a newly received information service application input from the user, the newly received information service application input comprising an input that selects the type of the newly received information service from a general selective dissemination of information service, a legal selective dissemination of information service and a similarity retrieval selective dissemination of information service; monitors newly received documents in accordance with the newly received information service application input; and informs the user of information on a newly received document that corresponds to an informing condition, the document processing unit comprising a processor, wherein if the general selective dissemination of information service is selected as the newly received information service, the document management system receives a retrieval expression from the user as the informing condition, determines whether a newly received document corresponds to the retrieval expression, and informs the user of the information on the newly received document if the newly received document corresponds to the retrieval expression, wherein if the legal selective dissemination of information service is selected as the newly received information service, the document management system receives an input that designates a reference document that was previously stored in the storage unit as the informing condition, extracts a representative value of the reference document, compares the reference document with a corresponding newly received document using the representative value, determines whether a legal status of the reference document is different from that of the corresponding newly received document, and informs the user of the information on the newly received document if the legal status of the reference document is different from that of the corresponding newly received document, and wherein if the similarity retrieval selective dissemination of information service is selected as the newly received information service, the document management system receives an input that designates a reference document that was previously stored in the storage unit as the informing condition, determines whether a newly received document is similar to the reference document, and informs the user of the information on the newly received document if the newly received document is similar to the reference document.