Dim result As String = "Spelled incorrectly."

If Me.Application.CheckSpelling(Me.Range.Text) = True Then
    result = "Spelled correctly."
End If

MessageBox.Show(result)

string result = "Spelled incorrectly.";

object startLocation = this.Content.Start;
object endLocation = this.Content.End;

bool spellCheck = this.Application.CheckSpelling(
    this.Range(ref startLocation, ref endLocation).Text,
    ref missing, ref missing, ref missing, ref missing, ref missing, ref missing,
    ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);

if (spellCheck == true)
{
    result = "Spelled correctly.";
}

MessageBox.Show(result);