Putting the subquery in the WHERE clause and restricting it to n.control_number means it runs the subquery many times. This is called a correlated subquery, and it’s often a performance killer.
It’s better to run the subquery once, in the FROM clause, to get the max date per control number.
SELECT n.*
FROM tblpm n
INNER JOIN (
SELECT control_number, MAX(date_updated) AS date_updated
FROM tblpm GROUP BY control_number
) AS max USING (control_number, date_updated);