Save them and run the left4dead2.exe executable directly (not through steam icon/games list). This should be located in a directory like C:\Program Files\Steam\steamapps\common\left 4 dead 2 demo, just like the first file above.
May have cracks in plastics, particularly around the hinges. May have major scuffs or scratches on screen. May have one or two dead pixels. May have cosmetic damage. May have letters heavily worn on keyboard. 2b1af7f3a8