price_letters.html.erb

# price_letter.pdf.erb
<%=
  require "prawn/measurement_extensions"
  require "prawn/table"

  pdf = Prawn::Document.new(
    :page_size => "A4", 
    :left_margin => 2.cm,
    :right_margin => 2.cm,
    :top_margin => 2.cm,
    :bottom_margin => 1.5.cm 
  )
  # logo
  logo = image_dir + 'logo.jpg'
  pdf.image logo, :position => :center
  pdf.font "Times-Roman"

...

  pdf.render
%>