1. A method comprising: controlling usage, at a client system, of an application program, wherein the usage comprises an operational functionality of the application program comprising at least one of editing or copying content of a document opened by the application program, the controlling step limits the application program's operational functionality in accordance to at least one rule stored on the client system, the at least one rule contains at least one expression used by the controlling step to control application program operation, the application program comprises a first modification and a second modification relative to the application program in unmodified form, the first modification comprises an interception feature, and the second modification comprises a usage control feature; and controlling access, at a server, to documents, wherein the controlling step limits document access operation in accordance to at least one rule stored on the server, and the at least one rule contains at least one expression used by the controlling step to control document access operation, wherein the controlling usage, at a client system, of an application program comprises detecting at the client system, via the interception feature of the application program, an application program operation corresponding to at least one low-level operation on a first document managed by the server associated with a first application program operation from a first application executing on the client system, and intercepting the application program operation corresponding to the at least one low-level operation, based on the detected application program operation by the interception feature, to prevent the at least one low-level operation from executing.