Convert all pages with Carrierwave::MiniMagick

convert_all_pages_to_pdf.rb

# MiniMagick::Image.format method by default converts only the first page.
# Carrierwave::MiniMagick.convert(:pdf) does not allow us to pass a second parameter page = nil.
# We need to paste in below code in the carrierwave initializer (or you may choose to extract it to lib folder)
# and use convert_all_pages_to_pdf in you uploader.

module CarrierWave
  module MiniMagick
    def convert_all_pages_to_pdf
      manipulate! do |img|
        img.format('pdf', nil)
        img = yield(img) if block_given?
        img
      end
    end
  end
end

Latest versions of CarrierWave should not have this issue.
carrierwaveuploader/carrierwave#1408