Hello, Dany,

I would like to follow up with  the following KB article which demonstrates a sample approach how to achieve text selection and copy functionality in chat messages: https://docs.telerik.com/devtools/winforms/knowledge-base/how-to-select-and-copy-text-in-chat-messages 

Note that this is just a sample approach and it may not cover all possible cases. Feel free to modify and extend it in a way which suits your requirements best.

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik