To be able to unlock the form you will need to have the FormsWorkflow Ribbon Add-In to MS Word. On the Ribbon there is a pad lock icon. To unlock the form click on the icon and you can now edit the document. If you want to fill in the form make sure to relock the form so you don't delete any necessary formatting.
The forms by default, download in a locked mode so they can be filled out by typing in it or using auto fill. The pad lock should show a closed, and when you unlock it, it will appear as if the padlock is open.