Upload a document attachment

Upload a file for a specific attachment on a document. This can be used when an attachment is of type file. You upload one file at a time via a multipart POST, and the file is associated with the given document and attachment id.

This can be used on documents that are in draft or have been sent, as long as they have not yet been signed or approved. Attachments can have restricted access or require a view or click before the signing can proceed.