You need to insert Badly before Bad in your Word table otherwise it will replace Badly by Goodly.
HTML
<asp:TextBox ID="txtDescription" runat="server" Text="Bad better Worst Best Badly Not" />
<br />
<asp:Button ID="btnSave" runat="server" Text="Save" OnClick="Save" />
I have used dummy table to store all the words that you have mentioned.
Namespace
using System.Data;
C#
protected void Save(object sender, EventArgs e)
{
DataTable dt = new DataTable();
dt.Columns.Add("Name", typeof(string));
dt.Rows.Add("Badly");
dt.Rows.Add("Worst");
dt.Rows.Add("Bad");
dt.Rows.Add("Not");
foreach (DataRow dr in dt.Rows)
{
this.txtDescription.Text = this.txtDescription.Text.Replace(dr["Name"].ToString(), "Good");
}
string description = this.txtDescription.Text;
}