Locating the demo:
To locate the demo you recorded or to place a demo file you just downloaded you’ll need to go into the tf folder of team fortress 2. Go to “C:\Program Files\Steam\steamapps\Login Name\team fortress 2\tf”
*.dem is the extension of the recorded demo.
Local Demo Store : Click Here
To watch the demo go into CONSOLE by pressing the tilde “~” key on your keyboard. Then type “Playdemo NAME” to watch the demo you recorded or downloaded.
When you are watching the demo hit “SHIFT+F2” to toggle on/off the demo control player. This will allow you to do basics such as fastforward/rewind, skip, stop, start. Also it will allow you to add texts, sounds etc for more advanced publishings.