There are very few extra features on the Logitech K840. It has media control hotkeys, as well as some shortcuts for apps, such as mail and calculator. Out of the box, F1 through F12 are function keys by default, but this can be changed within Logitech’s Options software to have the media controls as the default, and would require the use of the ‘fn’ key in order to access function keys.
One element that’s oddly missing is a Num Lock LED indicator. That said, if you have Logitech’s Options software installed, an on-screen pop up will let you know when it has been activated.