As I said before, you must leave.
You are happy as we all know.
Do as I say
He did not need to keep moving house, as his father had.
He is a foreigner, as is evident from his accent.
I checked the webster and longman. They says that "as" is used as relative pronouns in the first two sentences, which means "a fact/a thing that", while as conjunctions in the last two, which means "in the same way that".
I am confused by the meaning in these sentences. In my opinion, the third one can also be considered as pronoun, because it can be translated this way,
Do the thing which I told you to do.
And the second sentence can also be considered like this,
You are happy in the way we all know.
The other two sentences can also be misunderstood to me. So what's wrong with my understanding.