Media Library and open access to files

Dear support Team,
on a Wordpress Website for a client we have a membersarea, to which members only have access if they are logged in.
The client offers his members downloads (mainly .pdf and .xlx) which are linked in the restricted members area, but uploaded them into the media library. Thus the PDFs with mainly confidental information are public and even indexed by google.
Of course we know how to get them out the google index, but now we have the challenge to protect the PDFs in the Media Library, so only members who are logged in are able to see and possibly download them.
The long way would be to manually delete all files and use a downloading plugin for the members area,
the only problem is: we are talking about 300+ files which should be deleted, uploaded and linked again.
Thus our question is: Do you know a possibility how we can solve this issue maybe by protecting only the PDFs in the Media Library or is there a plugin which can help us?
Thank you very much!