The PDFs to merge, and the combined PDF's settings.
@type t() :: %Docspring.Model.CreateCombinedPdfRequest{ delete_custom_files: boolean() | nil, expires_in: integer() | nil, metadata: %{optional(String.t()) => any()} | nil, password: String.t() | nil, source_pdfs: [Docspring.Model.CombinedPdfSourceInput.t()] }