create a downloadable file after submit webform
This module may be used for your idea please use and try this module 

Webform2PDF

The Webform2PDF Drupal module is an extension of the Webform module. It can be used to generate PDF document from the results of a form. The generated PDF document can be attached to the form summary e-mail sent by Webform module, or it can be downloaded from the /Results/ page. Different PDF templates can be set for each form. The templates can be formatted with HTML tags, and they can be edited with WYSIWYG Drupal module, making the template creation easy and the templates highly customizable. The output documents will be created by using these templates.