How to include "File upload" field in the webform composite element? I have created a custom composite element, I want to include "File upload" field...The field is visible to the user and the file is uploaded. But it is nowhere saved.
Depends on the destination folder. This webform FAQ might help you.

Edit: Webform Composite Elements do not support File elements yet. Reference on drupal here 

Follow these issues (active as of 6/20/2017) to find release updates-
https://www.drupal.org/node/2883734
, https://www.drupal.org/node/2884624