1. The door is closed.
“is closed” indicates a state of being (closed is functioned as an adjective) — The door is not open; the door is shut.
2. The door is close.
“is close” indicates location — The door is nearby; the door is not far from here.
3. She has closed the door.
“has closed” indicates the use of present perfect tense in the sentence; “closed” is the past perfect of the verb close.
4. The door was closed by her.
“was closed” indicates the passive voice.
Active : She closed the door.
Passive: The door was closed by her.
5. They hid behind closed door.
“closed door” is a noun phrase; “closed” is served as an adjective modifying the noun “door”.
The word OPEN can be a verb and also an adjective. Take a look at the following sentences:
1. The door is open.
“is open” indicates an open state; the door is not closed (open is functioned as an adjective).
2. The door is opened automatically.
“is opened automatically” indicates the process of opening the door; it is a passive voice. (Opened is the past participle of the verb open).