If your original PDF file contained PDF form data, unfortunately this will not convert in the export process. This is because this is content (the form fields) in Acrobat after the file was created. There's no equivalent for that data within Word, so it is stripped out.
I'm sorry for the inconvenience.
This is a good idea - I added it to our Ideas list: http://forums.adobe.com/ideas/1549
If you'd like to see us impliment this in a future version, please go to the Ideas list and vote and/or add a comment.