I have install gem wicked_pdf for my app. For pdf generation in layout file "pdf.html.erb" include all css files
<%= Rails.application.assets.find_asset('user.css.scss').to_s.html_safe %>
<%= Rails.application.assets.find_asset('bootstrap_and_overrides.css.less').to_s.html_safe %>
<%= Rails.application.assets.find_asset('application.css').to_s.html_safe %>
It include a user.css.scss classes but not "twitter-bootstrap".
Hope this will work