The partial charges which are referred to in the textbook do not exist. They are just an analogy used to compare molecular dipoles with macroscopic dipoles (two charges $\pm q$ separated by some distance $d$).
As the diagram on the left points out, these charges are actually an asymmetry in the distribution of the electrons in the molecule, so that there is a difference between the centres of +ve and -ve charge, creating an electric dipole moment.
The formula for dipole moment is $p=qd$. If we take $d$ as the distance between the two nuclei in a molecule, then $q$ will be a small fraction of the electronic charge. However, if we take $q$ to be the total charge on all $n$ electrons in the molecule, then $q=ne$ is large and $n$ is a whole number. In this view it is actually $d$ that is a small fraction of the inter-nuclear distance.
Either way you look at it (small $q$ & large $d$ or large $q$ & small $d$) the value of $p=qd$ is the same, and it is this value which is important, not the values of $q$ or $d$.