PDF Rendering using partials

_partial.html.erb

<h5>Mi partial content</h5>
<%= @object.some_attribute %>

controller.rb

#action show
def show
  @object = Model.firts
  respond_to do |format|
    format.html
    format.pdf {render :pdf => "pdf_name}
  end
end

show.html.erb

<%= render "partial"%>

show.pdf.erb

<%= render :partial => "partial", :formats => [:html]%>

Cool it worked great :) . But I'm not getting the logic what is _partail.html.erb. How all files are interacting.