1. A document processing apparatus that determines whether or not a document image has watermark information embedded therein by use of character spacing, comprising: an input unit for inputting a document image; a character-spacing value extraction unit for extracting character spacing values in the document image; a calculation unit for calculating fluctuations in the character spacing values; and a determination unit for determining whether or not the document image has watermark information embedded therein by comparing a value of the fluctuations calculated by the calculation unit with a preset threshold value.