View a KYC document on file

Stream a document backing a reusable verification (the documentId values from GET /v1/phone-numbers/kyc reusable.options[].details[]), so the account holder can see what's on file before reusing it. Returned inline as application/pdf (uploads are normalized to PDF). Auth-scoped: a document is viewable only when its id is referenced by one of the caller's own numbers — otherwise 404.