Spending a lot of time figuring out how to execute javascript on your server isn't really going to help you -- all the javascript does is instruct the Flash object to generate the image, and POST the binary data to the webserver, so executing it on the server doesn't do any good unless you are also executing the flash on your server

Frankly, if you goal is that the user can trigger PDF generation (from the browser), then why don't you just use this same javascript to tell the Flash object to post the raw image back to your server, and then when your server gets the entire image, it can do whatever PDF generation it wants with it.

The Javascript hook provided by the OpenFlashChart API even has a callback mechanism so you can trigger a download (or a redirect to a download) of the generated PDF.