1. A computer implemented categorization method comprising: receiving a sequence of pages to be categorized; for each of a plurality of pages in the sequence as a current page: computing a page category score for each of a set of categories for the current page; computing a first bipage category score for each of the set of categories for a first bipage comprising a preceding page and the current page; computing a second bipage category score for each of the set of categories for a second bipage comprising a subsequent page and the current page; computing a first boundary probability that there is a document boundary between the preceding page and the current page; and computing a second boundary probability that there is a document boundary between the subsequent page and the current page; for at least one iteration, for each of the plurality of pages, computing a refined page category score for each of the set of categories for the current page as a function of: the first bipage category scores weighted by a first weighting factor, the first weighting factor being based on the first boundary probability; the second bipage category scores weighted by a second weighting factor, the second weighting factor being based on the second boundary probability; and the page category scores of the current page; and outputting information based on the refined page category scores for each of the plurality of pages.