app/views/admin/site_customization/documents/new.html.erb
<h2><%= t("admin.documents.new.title") %></h2>
<%= form_for @document,
url: admin_site_customization_documents_path do |f| %>
<%= f.file_field :attachment %>
<div class="margin-top">
<%= f.submit t("admin.documents.new.submit_button"), class: "button success" %>
</div>
<% end %>