the "External Window Handler" is part of Adobe Acrobat or the free Adobe Reader - it's built-in, and not something you can download as a separate module. Let's look at this from a different direction: What is the problem you are trying to solve? What error message are you getting, and what are you doing in order to get this error message? I assume you are trying to display a PDF file in the browser. Which version of Acrobat or Reader are you using? It needs to be either version X or XI with the latest patches installed for Windows 8.1
Karl Heinz Kremer
PDF Acrobatics Without a Net
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