Taken from the "Word Help" window
About reading layout view
If you are opening a document primarily to read it, reading layout view optimizes the reading experience. Reading layout view hides all toolbars except for the Reading Layout and Reviewing toolbars.
Note When you open a Microsoft Word document that you have received as an e-mail attachment, Word automatically switches to reading layout view. If you don't want to use reading layout view for e-mail attachments, clear the Allow starting in Reading Layout check box on the General tab of the Options dialog box (Tools menu).