is there a way to block access to a path

[Authority]

So as the title says. I've asked this before but never got an answer. I'm hosting some important dlls on my website. Currently, if they know what the path for the dll is, for example: "yoursite.com/important/sys32.dll" they can just download it. Is there a way to block their access to the path? I have a little program that needs access to the dll tho. And the only thing that should have access to the dll is my program. Does anyone have an idea how to achieve smth like this? Please tell me!