Hide URL in address bar

I
need to allow users to load documents in the browser such as:<o:p></o:p>

www.domainName.com/somefolder/somedocument.pdf<o:p></o:p>

But these are
sensitive documents and they need to be protected.  So I have 2
requirements:<o:p></o:p>

1)  Only
allow logged in users to access them<o:p></o:p>

2) Hide the
path<o:p></o:p>

What would be
the best practices in this case?<o:p></o:p>

Thanks.<o:p></o:p>