<%= form_tag preview_path(@document, format: :pdf), method: :get do %>
  <%= select_tag "id", options_from_collection_for_select(@templates, "id", "code"), include_blank: true %>
  <%= submit_tag "Download" %>
<% end %>

respond_to do |format|
          format.pdf do
            render pdf: "Labels " + @template.code,
            template: "documents/preview.pdf.erb",
            layout: 'layouts/pdf.html.erb',
            disposition: 'attachment', /* DIRECT DOWNLOAD */
            locals: {:document => @document},
            show_as_html: false,
            margin:  {   top:               @template.top_margin,                     # default 10 (mm)
              bottom:            @template.bottom_margin,
              left:              @template.left_margin,
              right:             @template.right_margin },
              paper_size: @template.paper_size
            end
          end
        end