securing pdf files in an application

Hi there.

Im trying to build an application that secures pdf files so that no one can upload them just by typing in the url.
They need to be in a secured directory and then accessed via a coldfusion page.
I have tried this but the only way I can seem to do this is via:

<cfheader
name="Content-Disposition"
value="attachment; filename=#filename#">
<cfcontent
type="application/unknown"
file="#filepath#">

Ive tried using application/pdf to display the page in the browser but all this seems to do is output the actual pdf code.
Any ideas?

Also thinking about storing the pdf's in a sql server database. Has anyone had any experience with this and also retrieving the pdf files?

Thanks Heaps