Protected view is a new option added in Office 2010 which keep us safe and secure in case from files originated from Internet as it may contain some sort of harmful ad unacceptable content. If we download any file from Internet adn try to open in let say in Word 2010 then it will prompt us that the particular file is originated from Internet location and disable editing in it. That file is kept in reading mode only and no editing is possible in it untill editing is disabled.
Word 2010 feature named as Protected view will ask us for “Enable Editing” and the editing will be possbible only if we trust the file and give indication to Word 2010 about our trust by clicking on Enable Editing.
Now if we click on this button “Enable Editing” then we are able to edit the file other wise not. So such features keeps us secure by disableing editing option in the file in case having any malicious activity or Internet originated.