Word's following standard behavior in accordance with the Apple Human
Interface Guidelines:
Clicking an application icon in the Dock should always
result in a window — a document or another appropriate
window — becoming active. If a document-based application
is not open when the user clicks the Dock icon, the
application should open a new, untitled window.
While an application is open, the Dock icon has a symbol
below it. When a user clicks an open application’s icon
in the Dock, the application becomes active and all open
unminimized windows are brought to the front; minimized
document windows remain in the Dock. If there are no
unminimized windows when the user clicks the Dock icon,
the last minimized window should be expanded and made
active. If no documents are open, the application should
open a new window. (If your application is not
document-based, display the application’s main window.)
Ref:
http://tinyurl.com/yux79o