Step 1 :
After factoring out $ x $ we have:
$$ x^{4}-12x^{3}-36x^{2}+432x = x ( x^{3}-12x^{2}-36x+432 ) $$Step 2 :
To factor $ x^{3}-12x^{2}-36x+432 $ we can use factoring by grouping:
Group $ \color{blue}{ x^{3} }$ with $ \color{blue}{ -12x^{2} }$ and $ \color{red}{ -36x }$ with $ \color{red}{ 432 }$ then factor each group.
$$ \begin{aligned} x^{3}-12x^{2}-36x+432 = ( \color{blue}{ x^{3}-12x^{2} } ) + ( \color{red}{ -36x+432 }) &= \\ &= \color{blue}{ x^{2}( x-12 )} + \color{red}{ -36( x-12 ) } = \\ &= (x^{2}-36)(x-12) \end{aligned} $$Step 3 :
Rewrite $ x^{2}-36 $ as:
$$ x^{2}-36 = (x)^2 - (6)^2 $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = x $ and $ II = 6 $ , we have:
$$ x^{2}-36 = (x)^2 - (6)^2 = ( x-6 ) ( x+6 ) $$