My custom pdf not working in sugarcrm 8

Ive been trying to generate an example pdf file in sugarcrm using the example code in the documentation in this link

and tried accessing it through this url:

http://sugarpro8.local.com/index.php?module=Meetings&action=sugarpdf&sugarpdf=clientpdf

here is the source code:

<?php

require_once('include/Sugarpdf/Sugarpdf.php');

class clientpdf extends Sugarpdf
{
    /**
     * Override
     */
    function process(){
        $this->preDisplay();
        $this->display();
        $this->buildFileName();
    }

    /**
     * Custom header
     */
    public function Header()
{
    $this->SetFont(PDF_FONT_NAME_MAIN, 'B', 16);
    $this->MultiCell(0, 0, 'TCPDF Header',0,'C');
    $this->drawLine();
}

    /**
     * Custom header
     */
    public function Footer()
{
    $this->SetFont(PDF_FONT_NAME_MAIN, '', 8);
    $this->MultiCell(0,0,'TCPDF Footer', 0, 'C');
}

    /**
     * Predisplay content
     */
    function preDisplay()
    {
        //Adds a predisplay page
        $this->AddPage();
        $this->SetFont(PDF_FONT_NAME_MAIN,'',PDF_FONT_SIZE_MAIN);
        $this->Ln();
        $this->MultiCell(0,0,'Predisplay Content',0,'C');
    }

    /**
     * Main content
     */
    function display()
    {
        //add a display page
        $this->AddPage();
        $this->SetFont(PDF_FONT_NAME_MAIN,'',PDF_FONT_SIZE_MAIN);
        $this->Ln();
        $this->MultiCell(0,0,'Display Content',0,'C');
    }

    /**
     * Build filename
     */
    function buildFileName()
    {
        $this->fileName = 'example.pdf';
    }

    /**
     * This method draw an horizontal line with a specific style.
     */
    protected function drawLine()
{
    $this->SetLineStyle(array('width' => 0.85 / $this->getScaleFactor(), 'cap' => 'butt', 'join' => 'miter', 'dash' => 0, 'color' => array(220, 220, 220)));
    $this->MultiCell(0, 0, '', 'T', 0, 'C');
}
}

here's an screenshot of the error message:

also my custom pdf file is in the path of /custom/modules/Meetings/sugarpdf/sugarpdf.pdfview.php

what did i do wrong here ?