demarches/app/views/letters/show.html.erb

<h2><%= @letter.title %></h2>

Rédigée par : <%= @letter.author %>
<% unless @letter.private_email %>
  (<%= @letter.email %>)
<% end %>

<div>
  <iframe src="<%= url_for @letter.document %>"
          type="<%= @letter.document.attachment.blob.content_type %>"
          style="width:1000px; height:800px;"></iframe>
</div>