Sure, the C# page on Texpad’s site shows you how to enable syntax highlighting by downloading the syntax definition files for C#, but even this isn’t necessary. Here is how you enable it for C# without downloading additional syntax files.
Open Textpad and click Configure > New Document Class.
The Document Class Wizard will be displayed. In the document class name box, type a name say, CSharp and click Next.
In the class members box, type *.cs and click Next.
check the enable syntax highlighting box. From the syntax definition file dropdown, select java.syn and click Next.
Now click Finish to create the new document class.
Open any of your .cs C# file(s) in textpad. If Microsoft has done as good a job on C# from Java as it did on SQL Server from Sybase -which I think it did – you should see all the C# keywords and syntax characters highlighted !