Permalink function Media uploads

I have basically a simple question, but i have been searching for the answer for two days. I still didn’t found any solutions. My hope is set on this forum.

My question:
Each document or picture i upload in my WordPress gets his own permalink. The problem is that i have certain documents which are not for publication. You can view each document by his own permalink now. The search engines like Google also show the permalink which makes it only worse. My question is: is it possible to edit or add some code to shut the automatic permalink function for uploaded Media down?

I hope someone has the solution for me!