secure files from direct url access

Hi first time poster

I have modx evo installed/configured and I have a secure section on my site with web logins working great. I however have a problem with a PDF file I want only accessible with these user behind the secure pages.
I set up a web link linking to the file but the problem is anyone not logged in can go to the direct URL
eg. www.example.com/modx/assets/files/pdf/document.pdf

I have tried setting htaccess on this directory but obviously it asks for htaccess password even when logged into modx. Also tried this plug in UsersToHtpasswd, thinking it might sync user passwords and wouldn’t prompt. Didn’t work.

Have tried using modx rev using static resources but same problem.

Is there anyway I can completely protect direct URL access, but logged in modx user have access?

Any insight would be very helpful
Thank you
Shazzed

Edit: modx evo 1.0.3 , apache webserver

Either store the .pdf files outside of the web space and use a snippet to generate a download, or store the .pdf files as BLOBs in the database and again use a snippet to generate the download.

Here are a few other options:
http://modxcms.com/extras/package/147
http://modxcms.com/extras/package/148

Thanks sottwell perfect!
Went with the first option worked great

Thank you for your reply.
Cheers
Shazzed