Do from is an ‘Indianism’, so use of this phrase must be referred to speakers of that dialect.
In Standard English† we use at with the verb do; the preposition phrase names the place where the work was performed:
I did my doctorate at the University of Wisconsin.
He did an internship at Microsoft.
We use from in this context with receive; the preposition phrase names the entity which conferred the gift:
I received my doctorate from the University of Wisconsin.
In ordinary speech, however, we use the verb get, which may take either preposition phrase (though at is probably more common)
I got my bachelors at Vanderbilt.
I got my bachelors from Vanderbilt.
With do we use at;
In a question, no preposition at all is needed, whichever verb you use:
Where did you do your bachelors?
Where did you get your bachelors?
Where did you receive your bachelors?
†By “Standard English” I mean English usage which will pass unnoticed with any educated native speaker—appropriate to its register and not dialectal, foreign, antiquated, or precious.
"We are to" means we are supposed to, "we have to" means we must.
a) We are to pay him the amount.
Means we are supposed to pay him the amount.
b) We have to pay him the amount.
Means we must pay him the amount.
Best Answer
It's "Have you returned from the conference?".
Be can be a helping verb with the -ing form of the verb (to express progressive tenses), not the -ed form.
For example: "I am returning", "she was returning", etc.
So, in interrogative mood, it would be "Are you returning from the conference?".
If you want to ask a question, but don't want to use a progressive tense, and aren't using any other helping verbs like have, will, should, you'll generally need to use do as a helping verb.
Did you return from the conference?