Problem
You are trying to use the pdfkit (here) in your rails application, and you configure it according to the configuration options for the rails 2.x in the config/environment.rb file. Although the application works, when you are trying to use the console you get the error:

no such file to load -- pdfkit (LoadError)

Solution
Make sure that:

require 'pdfkit'
in the config/environment.rb file comes after the line:

require File.join(File.dirname(__FILE__), 'boot')