1. A two-level document processing method preparing a downstream document on the basis of an upstream document, said upstream document being a document associated with a product and placed near a user, and said downstream document being a document associated with the product and placed near a maker, said method comprising the steps of: comparing the upstream document with an upstream deletion document including information which is particular to the upstream document and is unnecessary for the downstream document; selecting, from the upstream document and based on results of the step of comparing, a deletion candidate to be deleted from the upstream document until no more deletion candidate is found; and preparing the downstream document by performing deletion or non-deletion of the deletion candidate from the upstream document in accordance with results of the step of selecting.