# File lib/pdfkit/pdfkit.rb, line 58
  def to_pdf(path=nil)
    append_stylesheets

    args = command(path)
    invoke = args.join(' ')

    result = IO.popen(invoke, "wb+") do |pdf|
      pdf.puts(@source.to_s) if @source.html?
      pdf.close_write
      pdf.gets(nil)
    end
    result = File.read(path) if path

    raise "command failed: #{invoke}" if result.to_s.strip.empty?
    return result
  end