I have created a custom Webform Handler that takes the files uploaded by the user on a Webform and uploads them to the third-party file management system Box via Box's API. I want to also upload the Attachment PDF that is generated but I don't know how to get the file programmatically. I can click on the pdf links generated and they successfully download as expected. However, if I try to load that file programmatically, it is empty. If I manually navigate to the given path... there is nothing there. Where does this file live? How do I load it into my code? The link that is generated is: /webform/[form_id]/submissions/[submission_id]/attachment/[attachment_field__machine_name]/attachment.pdf