Please use the following code:

 

    // get the cute editor instance
    var editor1 = document.getElementById('<%=Editor1.ClientID%>');
    
    //Get the editor content  

    var editdoc=editor1.GetDocument();

 

    // attach Event
    if(editdoc.attachEvent)
     editdoc.attachEvent('onkeypress',HandleChange);
    else if(editdoc.addEventListener)
     editdoc.addEventListener('keypress',HandleChange,true);
   }