Choosing CMS or RAD tool?

Hello people and congrats for your wonderful forum!

I'm looking for a framework to develop a medium-sized application (an application like a document management system) and I would like to ask if drupal is the appropriate solution to my needs.

First of all how many time will I need to learn Drupal?
And of course is there any module/add-on in Drupal like a RAD tool? Is it customizable and flexible?

Thanks all of you for your answers.
Panagiotis