Apply bilinear transform to transfer function represented in zero-pole form. FS defines the sampling frequency. If z.Length < p.Length the routine will not add zeroes at -1 to match the number of poles unless AddZeros is True. 

Bilinear transformation is defined with the mapping:

       2   (1 - z^(-1))
  s -> - * ------------
       T   (1 - z^(-1))

Bilinear transform requires that the amplitude response of a continuous system is piecewise constant and can not be used to transform an analog differentiator to a digital filter (for example). Bilinear transform also does not preserve the impulse or the phase response [1]. 

References:  

[1] Theory and application of digital signal processing, Lawrence R. Rabiner and Bernard Gold. Prentice-Hall, 1975