Learn Farsi: من آن در زنگ‌زده را هیچ‌وقت باز نمی‌کنم.

It is a compound adjective made of the noun زنگ (rust) and the bare past participle زده (struck, from the verb زدن). Literally meaning rust-struck, it perfectly demonstrates the pattern of combining a noun and a past participle to describe a resulting physical state.

Wait, doesn't زنگ usually mean bell?

It does, but زنگ is a homonym that also means rust. You have to rely on context. A bell-struck door doesn't make logical sense, whereas a rust-struck door is clearly a rusted door. If you wanted to talk about a doorbell, you would use the noun phrase زنگ در.

Why does the object marker را come after the adjective instead of right after the noun در?

The object marker را must always follow the complete noun phrase that acts as the definite direct object. Because the specific object being acted upon is the entire phrase that rusted door (آن در زنگ‌زده), the را anchors to the very end of it.

Why is the verb باز نمی‌کنم negative when the English translation simply says I never open?

Farsi requires negative concord. This means that when you use a negative time word like هیچ‌وقت (never), the main verb must also take a negative prefix. Unlike in English where two negatives cancel out to make a positive, Farsi negatives work together to form a single negative statement.