To use the ExportPDF service, simply visit http://exportpdf.acrobat.com and click 'Sign in' at the top right corner. Enter your Adobe ID (email address) credentials to log into the service. As ExportPDF is web-based, you simply utilize the tool through your web browser. After you're logged in, you should see the ExportPDF interface, with a button saying 'Select PDF file..' to get the process started.
Please let us know if you have any questions.