X = stat factor for PPD
If you are using the "Develop PPD" rule, use the developed formula, if not, use the undeveloped formula, don't add them together.
Undeveloped, you get X * level
Developed, you get X * ranks
If you are using level bonuses, and if your profession is listed as getting a level based bonus to the PPD skill = Y
Undeveloped = (X * Level) + (Y * Level)
Developed = (X * Ranks) + (Y * Level)
If you have a PP multiplier, it affects the final total, the only exception being if you have something like the "Archetype" BGO which gives you x2 PP, then you don't multiply twice.
Example
Assume a character's total PP from whichever calculation you use is 24
If this character has an x3 multiplier, they have 24 * 3 = 72 pp
Example 2
This character is "Archetype" so they have 24 * 2 = 48 PP
If this character has an x3 multiplier, they do not get 48 * 3 = 144 PP
Use the "Stacked multipliers rule" which is to take each multiplier -1 and add them up, then +1. so:
x2 archetype + x3 PP Multiplier
(2-1)+(3-1)+1 = 1+2+1 = 4
So this character would have 24 x 4 = 96 pp
Note: The only instance I can think of where multipliers stack on one PC for PPD is the one I just gave with Archetype and a PP multiplier, you cannot for instance normally use two PP multipliers stacked.