Create Document
Creates a new Eversign document for electronic signature collection from one or more signers. You can create documents either: 1. From a template (use EVERSIGN_LIST_TEMPLATES to find available templates, then specify template_id) 2. From uploaded files (provide file URLs, base64 content, or file IDs in the files array) Documents can be sent immediately to signers or saved as drafts. Use sandbox mode for testing. Returns the document_hash which can be used to track and manage the document.