File - Add to Workbook - New Workbook

Ribbon bar. Select the Home tab. In the Output group, click Add to Workbook and from the menu, select Add to New Workbook to create a new workbook and add the current document to it.

Classic menus. From the File - Add to Workbook submenu, select New Workbook to create a new workbook and add the current document to it.

Note that in addition to adding the current document to a new workbook, you can select any currently open workbook from the list provided in the menu.