1. A data processing apparatus comprising: a page acquirer for acquiring a plurality of page data expressed in a page description language; an operator extractor for extracting operators describing character strings in a text format, at least one by one, from among the page data acquired by the page acquirer; an operator classifier for analyzing the operators extracted by the operator extractor and classifying those operators which contain particular characters indicating a sequence in the character strings and whose font information about the character strings coincide with each other, as particular operators; and a page order determiner for determining an order in which two or more of the page data containing the particular operators classified by the operator classifier are to be arranged according to the sequence indicated by the particular characters.