There are two ways to access the ExportPDF service. You can access the service through Adobe Reader (version 10.1 and newer) or via your web browser.
You can access the ExportPDF service within Adobe Reader by choosing File > Save as > Word or Excel Online. The 'Tools' Panel of Adobe Reader will open. Click the blue 'Sign In' text. Enter your Adobe ID (the email address you used when you subscribed to the service) and your password, then click the 'Sign In' button.
Once you're signed in, click the blue 'Select PDF File:' text to choose a file to convert. When the conversion is complete, you'll be prompted to save your converted document.
You can download the latest version of Adobe Reader here: http://get.adobe.com/reader/
Open your web browser and navigate to http://exportpdf.acrobat.com and click 'Sign in' at the top right corner. Enter your Adobe ID (the email address you used when you subscribed to the service) and your password to log into the service. After you're logged in, you should see the ExportPDF interface, with a button saying 'Select PDF file..' to get the process started.