Upload an existing file to Macro from base64-encoded bytes, up to 25 MiB decoded. Use for PDFs, images, Office files, and other files; use CreateDocument for generated text or native Macro spreadsheets. Encode actual file bytes programmatically; never invent or transcribe binary content. Returns a document ID after the bytes are uploaded; preview and indexing may finish asynchronously. Does not read local paths or fetch URLs.