A family of Microsoft word processing software products for creating web, email, and print documents.
From where did you open the document? Word may force Protected view on documents opening from an internet location. (Internet locations include mail attachments, of course.)
Another possibility is that the document opened in Read Mode (sometimes called "reading layout view"). You can prevent that from happening by clearing the option to "Open e-mail attachments and other uneditable files in reading view" at File > Options > General.