Bdtyktl

I recently received an offer from a company. The HR of the company called a few days back after the negotiations got over and said that they have a system of employing a third party to do a background check on all the joinees. I said I am okay with it. He further stated that I should be submitting all my original documents-right from my high school ones to the company at the same time I receive my offer letter and even before joining them on their first day. Also, he says that he will send me an official email for the same and that they will return the documents on the day of induction.

My guess is that he thinks that I will be using my offer letter to attend interviews and negotiate with other companies and if I get a better offer from others, I will be joining other companies and that acquiring documents gives them a control over this. I am not too comfortable with submitting my documents as i am not sure of how the next few months before joining them would turn out to be. Now, I want to know if this is the usual thing companies do and if I am overreacting or is it just not ethical of them to expect me to submit the original documents even before joining them. Also, how do I go about this?

The reason the HR gave for asking the documents was that the company spends some money on my background checks and they want to make sure that those are not wasted