notes.rb

require 'pdf-reader'

#doc = PDF::Reader.new(File.expand_path('~/Desktop/note-example.pdf'))
doc = PDF::Reader.new(File.expand_path('./book-mw-read-thru.pdf'))
$objects = doc.objects

def is_note?(object)
  object[:Type] == :Annot && object[:Subtype] == :Text
end

def annots_on_page(page)
  references = (page.attributes[:Annots] || [])
  lookup_all(references).flatten
end

def lookup_all(refs)
  refs = *refs
  refs.map { |ref| lookup(ref) }
end

def lookup(ref)
  object = $objects[ref]
  return object unless object.is_a?(Array)
  lookup_all(object)
end

def notes_on_page(page)
  all_annots = annots_on_page(page)
  all_annots.select { |a| is_note?(a) }
end

doc.pages.each do |page|
  notes = notes_on_page(page)
  next unless notes.any?
  puts "# Page #{page.number}"
  puts
  puts page.text[0..200].lines.map { |line| "> #{line}" }
  puts
  notes.each do |note|
    puts "  * " + note[:Contents]
  end
  puts
  puts
end