DYNAMIC ENABLING OF FUNCTIONALITY IN ELECTRONIC DOCUMENT READERS

Methods and apparatus, including computer program products, implementing and using techniques for digital rights management. In one aspect, a method is provided. The method includes receiving an electronic document, where the electronic document includes one or more content items, a set of usage rights defining one or more features to be enabled when the document is read by an electronic document reader, and a stored representation. The method further includes generating a representation of invariant content items of the electronic document, comparing the generated representation with the stored representation, and enabling features corresponding to the set of usage rights in the electronic document only if the generated representation and the stored representation are identical, where the features are features performed by the electronic document reader on the electronic document.