This repo contains a Powerpoint VSTO AddIn that adds a button to Powerpoint's toolbar. Clicking the button will add a digital timer textfield (e.g. 05:00) to the center of the active slide. When that slide is shown in a slideshow, the timer runs downto 00:00.
The repo belongs to the following blog post: https://thecolorofcode.com/2019/01/30/howto-create-a-powerpoint-addin-in-c/