how to open pdf files from a secure area on a website

[IRG]

I have a member only area on a website (I use php and mysql for it). There are some links to pdf files there. I need to open pdf files from these links (preferably in a new page). Is it possible to do it in such a way that they are secure (i mean that only people who are logged in can view them)? At present if someone knows a link to the files they can open them without logging in. If yes, what is the best way to do it?

Please help!!!!!!!!!!