Can anybody clear my doubts?

He is gone = He has gone

You are finished = you have finished

He is done… he has finished
He has done.. something…an uncompleted action

I am obliged…expresses gratitude (at least in westerns it does)
I have obliged = I have done as requested, ”I have obliged you…”

Can anybody tell me more on this?

I’m hardly an expert but this is how they are different to me:

You are finished
You, as a person, is finished. Something has happened to you to ‘finish’ you.

You have finished
You have completed a task.

He is gone
Something has happened to him to make him leave or go away.

He has gone
Something happened to make him decide to go away.

The number 1 sentences aren’t necessarily passive. “Go” is an unaccusative verb; it can’t be made passive. Unaccusative verbs can use either “be” or “have” – another example is “fall”: “It is fallen – it has fallen”.

I would say that your other 3 examples consist of “be” plus an adjective. However “I am obliged” can also be passive. I suppose “you are finished” could be passive, but I don’t know in what circumstances you would use it.

Ah, the messiness of language! A phrase like “He is done” can technically be passive, but it is not likely. We do not, except in colloquial use, talk about doing a person. It is more likely being used as an adjective, meaning the person is finished with some activity. “He has done x” means that the person has in the past done activity x one or more times.

Even in a sentence like “They were frightened” it is more likely that frightened is being used as an adjective than that it is passive voice. If the sentence is extended to something like “They were frightened by the loud noise” then it would be passive voice.

And if that is not messy enough for you, the “has” phrases can be used to mean the same thing as the “is” phrases. “He has finished” can be used to mean pretty much the same thing as “He is finished.”