[Amit]

Like what we see in the Microsoft office word, if i wrote “This is abble” will show me a red line under the word.

my project //C# , C sharp// is load text file in the Richtextbox and correcting the wrong words, everything is fine except this thing. so any information or details will be helpful for me.

[Abhey]

This is called spell checking. Google for “c# spell check” and there are a ton of resources available. If you try to implement and have issues, we should be able to assist more directly.