The are several methods available:
Go to the frame you want to freeze (press “end” key to go to last frame) and
press the snapshot icon (camera) under the preview screen; The snapshot will be added to the media room and can be added to the time line and the duration can be adjusted with the pointer on the frame open the menu with the right mouse and select from Edit Video -> Freeze frame; The snapshot will immediately be added to the timeline (and the media room) and the duration can be adjusted.
Ad 1: Has the advantage that you can give the snapshot file a name and point it to a specific folder
Ad 2: Is faster
If you have to add a freeze frame frequently, it makes sense to use option 2 and set a hot-key for freeze frame (I have set it to alt-f). Go to “Edit menu”, select “key board hotkeys” and “customize”, in the “workspace” tab you will find the Freeze hot key not set be default.