The details for the multi-site warning claim that we are attempting to access the host web server.
Why does calling this.external cause the document to "think" that the host web site has been accessed? This doesn't seem to make any sense.
I have a very simple PDF file that demonstrates this problem, but I don't see how to provide an attachment here in the forums. I can email it to you directly. You can reach me at email@example.com.
We have set up a crossdomain file. However, our experience is that the crossdomain file does not affect whether the multi-site warning is shown. The crossdomain file will determine whether access to the site is permitted, but the multi-site warning will show up regardless if Reader detects connections to multiple different sites.
Of course, in this scenario, we're not accessing multiple sites, so the warning seems spurious.