Topic: PDF and Ruby on Rails

What problems can arise when users hits the get_pdf action?
If there are problems, how can it be solved?

class PdfController < ApplicationController
  def get_pdf
    send_data Pdf.create(params[:contents])
  end
end

class Pdf
  def self.create(contents)
    make_pdf(contents) # takes 30 seconds to run
  end
end