Basically, you just need to set the SpellCheck.IsEnabled property to true. Like this:
TextBox textBox = new TextBox(); textBox.SpellCheck.IsEnabled = true;
You can find this property in the System.Windows.Controls and refer to it as follows:
using System.Windows.Controls;
Editorial: I would strongly suggest using WPF over Winforms if this is an option you can explore. Winforms had its day once, but for a more modern development, WPF is a much more powerful platform.
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