Frequency: The word is one of the 3000 most common words in English.
1.
pp is written before a person’s name at the bottom of a formal or business letter in order to indicate that they have signed the letter on behalf of the person whose name appears before theirs. ( BUSINESS )
...J.R. Adams, pp D. Philips.
2.
pp. is the plural of ‘p.’ and means ‘pages’. ( WRITTEN )
See chapter 6, pp. 137-41.