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 is load text file in the Richtextbox and correcting the wrong words, every thing is fine except this thing.
so any information or details will be helpful for me.

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I dont know if this is what you want but yes it should do the thing.

Don't forget to import the DLL so that you can access the required property.
TO IMPORT THE DLL DO THE FOLOWING: view-->solution explorer--> right click refferences--> add reference --> search the framework section and find it there

THANK YOU castajiz_2 for all what you do
just one more thing, do i need to link reference ((the text fille that i add it)) with the richtextbox ?
this is the first time i do this

I think not, Did you manage to do some extra work once you imported your dll?

Hello again
what i mean it is, the reference that i add is not working, do i need to add codes to make it run with the RichTextBox ? or there is a tool i need add it ?
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Okay, now i realize that I misslead you. I tought that you were working in WPF(basically an upgraded winform framework). I' ve googled how to implement that on windows form but there are quite complex solutions. If you can transfer your app to wpf that would be great. You could easily solve you problem usin wpf framework. Consider downloading visual studio express 2010. IT's free. I m not sure if you version supports wpf.

SharpDevelop support WPA, But i didn't learned WPF yet, i think it's using different codes from WA.Thank you castajiz_2 for you information. i really appreciate it.I will stop now and focus at the basic.

Thank you again