US Patent 9189467 Method and apparatus for annotating an electronic document

A method and apparatus to mark-up an electronic document (i.e., a second electronic document) that is superimposed on a first electronic document keeping the first electronic document unchanged. The second electronic document is optionally viewed concurrently with the first electronic document. The second electronic document is capable of being viewed or modified using different application programs so long as the different application programs process the format used by the second electronic document. The second electronic document is saved as a separate document independent of the first electronic document.