The method is very easy, just copy either the bottom or top application file depending on where your taskbar is oriented.
This is what SweatyFish says:
” Made a simple app to add a drop shadow to your taskbar. One .exe for a taskbar on the bottom, and one for the taskbar on top. Use whichever you need…
-Adjustable opacity (darkness)
-Option to run at startup
Right click the shadow to choose preferences or to close it.