Gemfile

source 'https://rubygems.org'

gem 'redcarpet'
gem 'pdfkit'

generate.rb

require 'redcarpet'
require 'pdfkit'

file = File.open(ARGV[0], "rb")
contents = file.read

options = [:hard_wrap => true, :space_after_headers => true, :autolink => true,
  :fenced_code => true, :gh_blockcode => true]

markdown = Redcarpet::Markdown.new(Redcarpet::Render::HTML, *options)


kit = PDFKit.new(markdown.render(contents),
                 :page_size => 'Letter')

if ARGV[1]
  kit.stylesheets << ' #{ARGV[1]}'
end

saved_pdf = kit.to_file(ARGV[0] + ".pdf")