PM vs necropsy

PM

verb
  • To project manage. 

  • To send a private message to (a participant in a chat room, etc.). 

necropsy

noun
  • The pathological examination of a corpse, particularly to determine cause of death. 

verb
  • The act of performing a necropsy. 

How often have the words PM and necropsy occurred in a corpus of books? (source: Google Ngram Viewer )