When the person who signs a document and has his signature preceded by
p.p. it means that he has been given the authority to sign the document on behalf of someone higher in the hierarchy.
For example, given a secretary authorized to sign a letter on behalf of the president of a company, the signature takes the form:
p.p. Secretary's Signature
President's Name
or
President's Name
p.p. Secretary's Signature
Commonly in practice, an alternative form is used:
Secretary's Signature
p.p. President's Name