窓 and 戸: windows and doors as action targets
Distinguish windows from doors and identify what is opened or viewed.
Looking through a window
窓 (まど) means window. 「窓から庭が見えます」 says the garden is visible through the window.
「窓の外を見ました」 means looking outside the window. Its target differs from examining the window itself.
Opening and closing a door
戸 (と) means door. 「木の戸を開けました」 says the speaker opened a wooden door.
「戸が閉まっています」 describes a closed door. It does not identify who closed it.
Keeping the targets separate
「窓は開いていますが、戸は閉まっています」 says the window is open but the door is closed. Do not transfer one state to the other object.
「戸を開けずに窓を開けました」 says the window was opened without opening the door. Read both objects and the negation's scope.
What was opened in 「戸を開けずに窓を開けました」?
Show the answer and why
The window. The sentence explicitly excludes opening the door.