It could be that they haven't protected the document and therefore it won't of activated properly as a form.
Depending on how they want you to submit your application this is something you can normally fix yourself. Go to view and then toolbars and open the one for forms. The far right button, with the padlock on, should be highlighted. If it isn't then click on it to protect the document (the other buttons should now be greyed out). This should active the form so that hitting tab goes between the required fields that need filling in, and hitting space on boxes or clicking on them with the mouse will cross them.