Gérald,

The key difference is Poser12 and Poser 13 use Python 3. The API changes are mostly additions. Scripts that worked on Poser 11 usually work once the typical Python2->Python3 code changes are made. 

The present Poser versions do not have a .pdf but there is online documentation:

http://www.posersoftware.com/documentation/12/index.htm#t=Poser_Python_Manual%2FMethods%2FPoserPython_Methods.htm&rhsearch=python&ux=search

The above is for Poser12. Initially it gives an error message but that is solved once you click a chapter.