1. A document processing method, comprising the steps of: (a) obtaining a document, dividing the document into a plurality of terms, and giving a syntactic index to each of the terms; (b) dividing the document into a plurality of sentences according to at least one type of punctuation marks contained in the document; (c) selecting a plurality of key syntactic indexes from the syntactic indexes, transforming each of the sentences into a preliminary key terms sequence according to the key syntactic indexes, wherein each preliminary key terms sequence includes at least one preliminary key term corresponding to the key syntactic indexes; (d) selectively expanding the at least one preliminary key term of a representative sentence of the document into an advanced key term; (e) determining at least one core candidate sentence from the plurality of sentences according to the preliminary key term and the advanced key term to form a core abstract of the document; (f) forming a matrix by a key term of the preliminary key term and the advanced key term and the preliminary key terms sequence of the Step (c); (g) performing a singular value decomposition of the matrix to obtain a weight of the sentence corresponding to each preliminary key terms sequence; (h) selecting at least one of the sentences as an auxiliary candidate sentence according to the weight, and combining the at least one auxiliary candidate sentence into a supplementary abstract of the document; (i) receiving a compression ratio, and calculating the number of sentences in an abstract according to the compression ratio; (i) determining whether or not the number of sentences contained in the core abstract is smaller then the number of sentences of the abstract; (k) selecting the sentence from the core abstract having the number of sentences of the abstract as a displaying abstract of the document, if the determination of Step (i) is negative; and (l) selecting and merging the auxiliary candidate sentence which is not a repeat of the core abstract from the supplementary abstract into the core abstract to form the displaying abstract of the document if the determination of Step (i) is affirmative.
7. The document processing method of claim 1 , wherein the Step (e) further comprises the steps of: (e1) giving a first weight and a second weight to the preliminary key term and the advanced key term respectively; (e2) calculating a score of the preliminary key terms sequence containing the preliminary key term according to the first weight, and then calculating a score of a sentence containing the preliminary key terms sequence according to the score of the preliminary key terms sequence, and selecting a plurality of sentences according to the calculated score of each sentence; and (e3) combining at least one of the selected sentences into the core abstract.