```ruby
# config/initializers/pdfkit.rb
PDFKit.configure do |config|
  config.wkhtmltopdf = File.expand_path "../../bin/wkhtmltopdf-linux-amd64", __FILE__
  # config.default_options = {
  #   :page_size => 'Legal',
  #   :print_media_type => true
  # }
  # config.root_url = "http://localhost" # Use only if your external hostname is unavailable on the server.
end
```

Add missing require for pdfkit
user
```ruby
# config/initializers/pdfkit.rb
require 'pdfkit'
PDFKit.configure do |config|
  config.wkhtmltopdf = File.expand_path "../../bin/wkhtmltopdf-linux-amd64", __FILE__
  # config.default_options = {
  #   :page_size => 'Legal',
  #   :print_media_type => true
  # }
  # config.root_url = "http://localhost" # Use only if your external hostname is unavailable on the server.
end
```
assistant