Criando Manifest específico para cada Layout

_pdf.html.erb

<!-- layouts/_pdf.html.erb -->
<%= stylesheet_link_tag "pdf_manifest", media: "all" %>

Criando Manifest específico para cada Layout-README

Crie a pasta stylesheets/pdf
Coloque os .css.scss que deseja lá dentro

Crie um stylesheets/pdf_manifest.css.sccs
Inclua os .css que precisar no manifest (*= require)

Adicione a regra de compilação no production.rb

Carregue o manifest que deseja no layout específico.

pdf_manifest.css.scss

/*
 * This is a manifest file that'll automatically include all the stylesheets available in this directory
 * and any sub-directories. You're free to add application-wide styles to this file and they'll appear at
 * the top of the compiled file, but it's generally better to create a new file per style scope.
 *= require_self
 *= require_tree ./pdf
*/

production.rb

# Precompile additional assets (application.js, application.css, and all non-JS/CSS are already added)
config.assets.precompile += %w( pdf_manifest.css )