3. The document information search method according to claim 2, wherein: a repetition of a same character is omitted in extracting said single character while extracting said single character or character strings from said text file, and character strings other than a search object included in said extracted character string is omitted in said character string extraction.
2. The document information search method according to claim 1, wherein: said presearch file is generated by extracting a character string composed of a combination of certain single characters or connected plurality of characters from said text file to generate a character code or character strings code indicating an existing information of said characters or character strings, or placing a coding conversion to said character code or character string code.