What hook should I use to alter the File Upload field in Webform 7.x-4.16 In Drupal 7 Webform file field, might there be a way to access the link provided after the a file is uploaded? 

The reason is that we have a hot-folder/watch-folder process that runs, cleans a file, converts DOCs to PDFs, checks for accessibility, etc. I'd like to link to converted version of that file. 

We want to allow the user submitting everything to ensure their document is converted properly before they click the submit button.
I believe you could go far with hook_form_alter in drupal 7. Unless you're implying a multiple step webform where some webform hook may apply.

Browse over the webform.api.inc file in the module folder and if none of the hooks sound good for your needs try a simple form alter.