Allow Access To Directory if Logged Into Wordpress


I have a wordpress site installed in the root folder of a site. Beneath the root folder is a /docs folder with a bunch of older html files. I’d like to only allow wordpress logged in users to be able to have access to those /docs html pages (not to be confused with wordpress ‘pages’).

I have a Wordpress ‘portal’ page which displays links to the /docs pages if the visitor is logged in. I would also like to put in a textual search function (which I know how to do) so logged in visitors can get a list of relevant /docs pages

So… How do I allow logged in visitors to ‘see’ the /docs pages for both links and searches while denying access to outsiders? I don’t want to have to redo all the old html if possible (if I have to do -that- I’ll just import them into a wordpress taxonomy—but I hope to avoid that!)