The "P" command is used to write the text in the editing
  buffer to the output file and read the next page of text
  from the input file to the editing buffer.  Common forms
  of the command are:

      P  Write the current buffer to the output file
         and get the next page
     5P  Write the current buffer, plus the next four
         pages from the input file, to the output file,
         then read the next page from the input file
         into the editing buffer