Install Friendly ID

gem 'friendly_id', '~> 5.1.0'

bundle
rails g migration AddFriendlyIdToDocuments

# Newest migration file
def change
  add_column :documents, :slug, :string, unique: true
end

rake db:migrate

# Model
class Document < ActiveRecord::Base
  extend FriendlyId
  friendly_id :title, use: :slugged
end

# Controller
Document.friendly.find(id)

Document.find_each(&:save)

ActiveAdmin.register Document do
  before_filter :only => [:show, :edit, :update] do
    @document = Document.friendly.find(params[:id])
  end
end