KTextEditor provides a powerful text editor component that you can embed in your application, either as a KPart or using the KF5::TextEditor library (if you need more control). The text editor component contains many useful features, from syntax highlighting and automatic indentation to advanced scripting support, making it suitable for everything from a simple embedded text-file editor to an advanced IDE.
WWW: https://projects.kde.org/projects/frameworks/ktexteditor