The ribbon contains several options for displaying multiple open windows.
Enabled by default, drawing file tabs are displayed between the ribbon and drawing area. Click a file tab to switch to that drawing.
In addition to switching between drawings, you can also do the following from the file tab menu:
Selects a window if multiple files are open.
Arranges windows in horizontal, non-overlapping tiles.
Arranges windows in vertical, non-overlapping tiles.
Overlaps windows, leaving title bars visible.