I'm fairly certain that you can only do that if you write an Add-In. Dispatch only reads from the selected file(s) but can write to any file (if it is fully specified - complete path).
If this is actually possible then I would love to know how!
I agree with Tim,Its not possible to read variable from a file other than the active Doc (Selected file).Only and Add-in can help you in this case.
Thanks Tim, Thanks Ravi..
My expectation about Dispatch was more powerfull.. Some little developments are going to be enough to be free from API..