If you are talking about docs that are not open, you can go to Recent on the File tab... you can pin documents to the Recent list on the File tab, so the shortcuts to them stay even if they haven't been recently opened. Or you can easily create a macro and add a button to the Quick Access toolbar or Ribbon, or a custom keyboard shortcut.

For docs that are already open, on the View tab, you can Switch between open docs, or Arrange documents.