I think the key question is: does your choice of FrameWork, Language, and GUI resources toolkit and its API, give you some visual tools that will immediately help you write a rich-text editor, or a simple Text editor.
imho, .NET, C#, and your choice of WPF, or WinForms "flavors," offers you both rich- and simple- TextBox Controls to use that have many powerful features you can further develop to create advanced functionality.
There are many examples of WinForm RichTextBox based word-processors on CodeProject, and other sites. I am sure WPF has similar resources.
Take a look at Pavel Torgashov's 'Fast Colored TextBox for Syntax Highlighting' [^
] for a fine example of what you can build using the WinForm RichTextBox.
This recently updated CP article 'HandlEdInput - Powerful and Highly Customizable Input Handler for TextBox, RichTextBox and ComboBox' provides a powerful set of tools you can use to filter text input to do things like make a TextBox that can only accept a valid web URL: [^