The project is open-source. You can download the source and build the DLL from the PavelTorgashov/FastColoredTextBox GitHub repository .
Optimized for both small files and very large files. FastColoredTextBox.dll
Supports built-in languages (CSharp, VB, HTML, XML, SQL, Lua) and custom highlighting. Code Folding: Allows collapsing/expanding code blocks. The project is open-source
Includes Undo/Redo, WordWrap, and Find/Replace. How to Use It (Implementation) FastColoredTextBox.dll