No, you don't have to pay all fee of  4 years B.Tech as you you will have to pay fees semester wise in most of the colleges and in some of the colleges they take fees yearly. I have taken two cases as I don't know in which manner your college is taking fees.

And, for the documents nowadays most of the colleges take soft copy of documents from students. In  case, if your college have your original documents you can request your HOD or principal or administrative officer whoever can give you your documents they will surely give you if your reason to leave college is genuine .

Hope this answer helps you.