#!/usr/bin/env ruby require "prawn" require "prawn/security" pdf = Prawn::Document.new pdf.text "Hello, world!" pdf.encrypt_document :permissions => { :print_document => false, # :modify_document => false, :modify_contents => false, :copy_contents => false, :modify_annotations => false, } pdf.render_file(File.basename($0, ".rb") + ".pdf") 「:modify_document」でなく「:modify_contents」が正しそう