1. A method for enabling one or more operations in an electronic document reader, comprising: receiving an electronic document, the electronic document including one or more invariant content items, one or more modifiable content items, a set of usage rights defining one or more operations to be enabled when the document is read by an electronic document reader, and a stored representation, the one or more operations, when enabled, modifying at least a part of the electronic document; generating a current representation of the invariant content items of the electronic document, the generating comprising digesting the one or more invariant content items according to their complexity, wherein digesting the one or more invariant content items comprises recursively digesting the one or more invariant content items, wherein the invariant content items are organized in a layered structure within the electronic document; determining that the current representation and the stored representation are identical; and based on the determining, enabling the one or more operations features corresponding to the set of usage rights in the electronic document.