Answer
$a^2b^2-c^2d^4$
Work Step by Step
Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms, the given expression, $
(ab+cd^2)(ab-cd^2)
,$ simplifies to
\begin{array}{l}\require{cancel}
(ab)^2-(cd^2)^2
\\\\=
a^2b^2-c^2d^4
.\end{array}