Replace word while reserving first letter case

Window -> Door window -> door Windows -> Windows windows -> windows

Input

She opened a Window to let in some air. I looked out the window and saw a deer.
He stood at the window, moodily staring out. He led her to the Window.
He used vinegar and water to wash the windows. He accidentally broke a window.
Can you roll down the car window. The Windows along 5th Avenue were all decorated for Christmas.
I saw a beautiful dress in the window. He sits behind a Window and sells movie tickets.
Make sure the address shows through the Window in the envelope. A window opened in the fog and we could finally see the ocean.

Output

She opened a Door to let in some air. I looked out the door and saw a deer.
He stood at the window, moodily staring out. He led her to the Window.
He used vinegar and water to wash the windows. He accidentally broke a window.
Can you roll down the car window. The Windows along 5th Avenue were all decorated for Christmas.
I saw a beautiful dress in the window. He sits behind a Door and sells movie tickets.
Make sure the address shows through the Door in the envelope. A door opened in the fog and we could finally see the ocean.