Hi
From time to time we argue about this in our office. 'Per procurationem' means 'through the agency of', and many sources (including the Oxford Concise Dictionary) advise that the 'pp' comes before the name of the person signing. Some in my office continue to put the pp before the name of the person not signing, as although they acknowledge that this is formally incorrect, people will think them incorrect is they do it the correct way. At the moment, I am still holding out for putting it before the name of the person signing.