Build a Software

To work with Text, Audio, Images, and Video files, I think your best bet is using WPF to build your software. WPF supports all of these file types. If you search C# Corner for keywords like "WPF Text", "WPF Video", "Image in WPF" etc, you will find articles on these topics. Then you will have to learn and make one software out of all that.

To make it like PowerPoint where you can insert an object that can hold a file type, you will have to do extra work. Your WPF Window will work as a placeholder of controls and you can drag and drop an Object control (that you will create) and this object can then be the surface to hold other objects.

Hope this gives you a direction. Good luck!