- Halló la puerta abierta / cerrada.
is ambiguous, as it can mean:
1.a. He/She found the door open / closed (= He/She found that the door was open / closed / He/She found the door to be open/closed)
1.b. He/She found the open / closed door (= He/She found the door that was open / closed)
If the interpretation is 1.a., "abierta/cerrada" in sentence (1) is an object complement, that is, an attribute that refers to the direct object but does not form part of it. If the interpretation is 1.b., "abierta/cerrada" in sentence (1) modifies the head of the direct object, that is, "puerta". Unlike in interpretation 1.a., in interpretation 1.b. "abierta/cerrada" forms part of the direct object.
To disambiguate, the only possible way I can think of is to expand the structure:
1.a. Halló que la puerta estaba abierta/cerrada.
1.b. Halló la puerta que estaba abierta/cerrada.