Difference between NPV and PDV

What is the difference between Net Present value and present discounted value when periods are given in infinity $\infty$ . Both are then equal to $\frac M r$?

NPV and PDV are two different names for the same concept. If you were to receive M every year and the discount factor is $\delta$ then NPV = PDV = $\sum_{i=0}^{\infty}\delta^i M= \frac{M}{1-\delta}$.