1. A method for preparing an aggregate document comprising: attempting to retrieve data pages of the aggregate document; generating an instance signature for a first instance of a data page retrieved for inclusion in the aggregate document; comparing the instance signature to a baseline signature associated with a second instance of the data page; calculating a similarity value in response to the comparing, the similarity value indicating a degree of similarity between the first instance and the second instance of the data page; and determining whether to include, delete or bypass the data page in the aggregate document based on the similarity value.