Please give the following query a try. In the Assign activity:
dt3 = (From row1 In dt1.AsEnumerable()
Join row2 In dt2.AsEnumerable() On row1("Code").ToString() Equals row2("Code").ToString() Into grp = Group
From g In grp.DefaultIfEmpty()
Let status = If(g Is Nothing, "", g("Status").ToString())
Select dt1.Rows.Add(row1("Sl No"), row1("Code"), row1("PD_D1"), g("PD_D2"), status)).CopyToDataTable()