如何在Laravel传递参数下载PDF

Question

Here is my function in Laravel. I show you a small piece of code. I try to download a PDF document, but I could not download. What is the issue?

function case(){
    $dr_case_id = '1';
    $this->generatePDF($dr_case_id);
}

public function generatePDF($id)
{
    $view_case = Dr_Case::find($id);
    $pdf = PDF::loadView('fm.fm_pdf_case_report', ['view_case'  => $view_case ]);

    return $pdf->download('standpharm.pdf');
}