I'm not sure at which PDR version this came in (I only have PDR 15) but try using the little orange tabs to each side of the timeline scrubber. Grab one and drag it outwards and you'll see your selected area highlighted in orange on the timeline. You can right click anywhere in the selection and choose to produce the selection. Once completed the newly produced file appears in your media room and can be used as you would any other item in there.