This is a very controversial question among grammarians.
Many say past participle forms which are very often used by people just like the one you have brought up here are forms of passive voice. other grammarians say they are linking verb+ past participle form as adjectives.
However, grammarians like Marcella Frank believe that we cannot distinguish all of them, but the ones which are not followed by the preposition "by" when the doer/agent is mentioned could definitely be considered adjectives. An example could be "I'm interested in the book."
so this is something that cannot be settled in the English grammar well; of course, this is the view of a descriptive linguist, but prescriptive linguists would probably say these are forms of passive voice.