@spec fields(source()) :: {:ok, [PdfElixide.Form.Field.t()]} | {:error, term()}

Extracts form fields from the given PDF document or editor.

@spec fields!(source()) :: [PdfElixide.Form.Field.t()]

Extracts form fields from the given PDF document or editor, raising an error if it fails.

@spec set_value(PdfElixide.Editor.t(), String.t(), PdfElixide.Form.Field.value()) ::
  :ok | {:error, term()}

Sets the value of an existing form field on the given editor.

The value uses the same tagged-tuple shape returned by fields/1 (e.g. {:text, "Jane Doe"}, {:boolean, true}, nil).

@spec set_value!(PdfElixide.Editor.t(), String.t(), PdfElixide.Form.Field.value()) ::
  :ok

Sets the value of an existing form field on the given editor, raising an error if it fails.