An apparatus and a method for electronically displaying music scores use a music object file format to store and display music scores. A music score file is translated into a music object file. The music object file includes music data structures that correspond to notation objects that represent music symbols of a music score. The measure is the fundamental grouping unit. The music data structures are processed to form a page image that includes the notation objects of the music symbols to be displayed. An annotation is input to a touch sensitive display using one's finger or a stylus and displayed overlaying the displayed music score. Modifications to a displayed music score include transposing, resizing, expanding, and marking measures.