It sounds like you are reading in single page mode? We do keep the zoom level for "Continuous" viewing, but we do not preserve it for single page viewing. The presumption has beent that zoom is useful for enlarging specific content on a page and that this wouldn't be consistent page to page. It sounds like you have a document where you'd like to keep the same zoom. Is this to clip the margins of a document you are reading? Can you share the document with us at email@example.com?