How to give read only access to controlled document in uncontrolled space.

Hi,

I have a SharePoint site with strict permissions that has a lot of controlled documents stored in it. But there are files that I want to give to other internal customers. I dont want them to be able to edit them as they are controlled but they need the information on them. So I have made an open sub site that the customers can view to find these documents. 

Is there a way I can have a link to a read only copy of a file that is stored in a subsite that customers don't have access to?

I hope this makes sense. im pretty new to sharepoint so any help is appreciated.

Sam