i am trying to do something similar. when user requests a pdf file, i check if user has access to the file. if no access, redirect user to some other page. i am using HttpModule. 

public void Init(HttpApplication app)
        {
            app.BeginRequest += BeginRequest;
        }
        public void Dispose()
        {
            

        }
        private void BeginRequest(object source, EventArgs e)
        {
            HttpApplication app = (HttpApplication)source;
            //check user has access to requested file
            //if no access, redirect to errorpage
        }

 my problem is when pdf file is requested, BeginRequest method isn't called when debugging in IIS settings. it is called if i debug in website setting. i have registered the httpmodule in web.config file and
and also mapped .pdf extension  aspnet_isapi.dll. so in IIS settings, pdf file is displayed even user don't have access to it. what am i missing? this thing is driving me insane........... [:@]

any suggestions appreciated.