You need to log in. I assume you are using Adobe Reader and you want to convert your PDF document from within Reader. There should be a login option, once you click on that, you log in with your Adobe ID:
However, in my experience, it's more reliable to upload the PDF file manually to http://exportpdf.adobe.com, wait until the file is converted and then download the Word or Excel file.
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...
http://www.khkonsulting.com