When more than one drawing is open there are several ways to switch between them, here's the list:

1 - Hold the CTRL key and press the TAB button to cycle through the open drawings.

2 - Use the Window menu pull-down and select from the list.

3 - Enter TASKBAR at the command line and set the variable to 1.  Open files will now appear on the Windows Start Bar as separate listings to select.

4 - Enter TASKBAR at the command line and set the variable to 1.  Open files can then be selected by holding down the ALT key and pressing the TAB key as needed to cycle through the open files.