g1smd - 6:42 pm on Jul 6, 2011 (gmt 0)
The canonical LINK element syntax varies minutely with DOCTYPE.
<link rel="canonical" href="http://www.example.com/">
<link rel="canonical" href="http://www.example.com/" />
Always use "example.com" in the forum to stop the auto-linking function.
If you use Apache hosting you can quite easily amend the HTTP headers using .htaccess or PHP.
One thought is that if you add canonical information to the HTTP headers before the PDF file is sent, the canonical element in this case pointing to the URL for the HTML version, if Google finds another copy of that exact same PDF document elsewhere on the web, it might also associate it with the URL for your HTML page.
WebmasterWorld threads are often indexed in less than 60 seconds. :)