I have an issue on a Windows 7 PC using IE8 and Adobe Reader 9.3. While viewing a PDF file in Reader, and clicking on a URL link in the PDF, nothing happens unless a browser window is already open. It doesn't matter if the browser is Firefox or IE8, although IE is the default browser. When no browser is running, nothing occurs, not even an error or Enhanced Security message. I've verified that the "Create links from URLS" is selected.