Can't Extend Method From Module

I've extended the Form Helper module into a class. However, I received the undefined dom_class method error. So I solved that by including the module instead. This fixed the dom_class error but now I receive the error undefined form_for error. How do I fix this and be able to use form_for in my class?

class Form
  extend ActionView::Helpers::RawOutputHelper
  extend ActionView::Helpers::TagHelper
  extend ActionView::Helpers::FormHelper


  def self.generate
    form_for([@projectdoc], :html => { :multipart => true, :remote => true, :controller => "projectdocs", :action=> 'item_create', :id => 'file-dropzone', :class => 'dropzone',:method => 'post'}) do |form|
      form.file_field(:doc, :style => "visibility: hidden; position: absolute; top: 0px; left: 0px; height: 0px; width: 0px;")
    end.html_safe
  end
end