Processing google file requests

We have a web site which contains, among other information, some pdf files. If somebody finds one of these pdf docs in google, in addition to the window containing the file, we want a new window showing our site's main page to be opened. We wonder if there's a way to make it. Can we write a dll which detects google requests and process them? In this case, how?. Is there another way to make it?

Thanks in Advance

If you could get a PHP script with a .pdf extension to be parsed as a PHP script then you could check the referrer. You'd create this PHP script so that it was called exactly the same as the current PDF file and save it in place of the current PDF document. You'd need to move the actual PDF files elsewhere and make sure that they weren't being parsed as PHP scripts. The PHP script would check if the referrer is from Google, and if it was, it could redirect to another page where the actual PDF file and the main site could be opened in two windows.

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Of course, any scripting language should work for this. I just mentioned PHP because that's what I'm most familiar with.