Adjective vs noun.

I have noticed that any verb that comes after the auxirally verb have and has is being treated as the past participle and the verb that do not follow directly these auxirally verbs are used as an adjective for instance:

  1. I have completed the task.( to me completed is pp
    2.He was amazed by the action.( amaz is an adjective)
    Sometimes to me some verbs behaves as an adjective and also as a noun.
    Please if I am wrong assist. Thanks

Your question is confusing to me. The main difference between these two sentences is the first is in active voice while the second is in passive voice.

Notice these two sentences:

  1. I have completed the task.

  2. The task was completed by me.

I agree that “completed” in sentence #2 is a bit like an adjective, but it is still being used asa verb. For completed to be a “real” adjective, you could write something like “I turned in my completed task”

This website has some good information that is presented clearly: