config.dropdownmenumanager: {
          'PasteMenu': {
            items:[{
              name: 'Paste',
              command: 'paste'
             }, {
               name: 'PasteText',
               label: 'Paste as text',
               command: 'pastetext'
             }, {
               name: 'PasteFromWord',
               label: function(){ // If the menu is opened and the promise has not been resolved the menu label is equal to the name
                  return Promise.resolve(function(){
                    return 'Paste from Word'
                  });
               },
               command: 'pastefromword'
             }],
            label: {
              text: 'Paste',
              width: 45,
              visible:true //default value
            },
            iconPath: 'paste' //You can use global icons or absolute path to the icon
            toolbar: 'clipboard', // to specify toolbar group for button
          }
}

{
  toolbarGroups: [
    {name: 'clipboard'} // now includes paste dropdown menu
  ],
  removeButtons: 'Paste,PasteText,PasteFromWord'
}