Import of form in Formscentral depends on how it was created. If you used LiveCycle designer to create the original form then it cannot be imported. However, if the form is created in Acrobat then you can import it by clicking on Import PDF form under Create New form heading.
Note: In the imported form you may edit the position of the submit button, but other design edits to the imported form will need to be made in the tool used to create that form.
Hope that helps, let me know if you have any other question.
Thanks for the help..