Zooming

Set the default zoom factor for displaying the PDF document, which defaults to 1.0 and is limited to the range of 1.0 to 5.0.

CPDFReaderWidgetController? _controller;

Scaffold(
  resizeToAvoidBottomInset: false,
  appBar: AppBar(),
  body: CPDFReaderWidget(
    document: documentPath,
    configuration: CPDFConfiguration(
      readerViewConfig: const ReaderViewConfig(pageScale: 1.0)),
    onCreated: (controller) {
      setState(() {
        this._controller = controller;
      });
    },
  ));

Setting zoom via CPDFReaderWidgetController:

_controller.setScale(1.0);