Sorry about that, Evan. Dealing with security is a pain.

You'll have to setup an Application pool and have the application pool run under an account that has limited access but enough to access the network share.

So you'll go into IIS Console, expand Application Pool nodes, right-click and add new application pool - give it appropriate name.

Right-click on you're newly created pool and select properties.

Select the Identity Tab and use an account that has access to the network share where you're PDF files are located. Click on OK to close the window.

Next, right-click on your website and select properties.

Select the Home Directory Tab, in the application pool field select the newly created application pool.

Hopefully this will work for you - sorry about having you chase ghost with the previous post.