20. The system of claim 13 , wherein the one or more computers comprises one personal computer, and the personal computer comprises the user interface device.
13. A system comprising: a user interface device; and one or more computers operable to interact with the user interface device and to: obtain an electronic document in a first format, the electronic document comprising a graphic object represented using a main dataset and a private dataset; normalize the main dataset of the graphic object of the electronic document stored in an object model in memory; compute a checksum for the normalized main dataset of the graphic object; compare the computed checksum with a stored checksum located in the private dataset of the electronic document; and convert the electronic document from the first format to a second format based in part on a result of the comparing, wherein the converting comprises, when the computed checksum and the stored checksum do not match, propagating a change from the main dataset to the private dataset.