Since there was no reply to my question I figuered it out by myself. Perhaps this is going to be useful for someone else. I am going to explain it on explicit Euler example. The stability region for Euler is written as |(1,0) Padé | ≤ 1. We look at the table in Wikipedia (title: An example – the exponential function) and take the equation which is located in 1st row and 0th column ((1+z)/1). We insert some complex numbers as z and check if the absolute value of the result is smaller than 1. We then plot z on a plot with real x-axis and imaginary y-axis. The result of Euler example is shown in the attachement.