Abstract: A display apparatus including a communicator configured to perform data communication with a content server and to receive at least one of a main document and a sub document related to the main document; a document analyzer configured to extract a keyword having a high frequency of occurrence from the main document and to determine a head keyword for generating a summarized document from the extracted keyword with reference to the received sub document; and a processor configured to determine a reliability of each sentence of the main document based on the head keyword, extract a sentence that matches a predetermined condition with reference to the determined reliability, and analyze a structural format of the extracted sentence so as to re-configure a word that forms the sentence and generate a summarized sentence, thereby generating a summarized document where information and logical cohesion have been obtained.