Events uses the Dompdf (opens new window) library implemented in Craft Commerce to generate PDF files. You can manage some of the Dompdf options through a configuration file.
Create a file named events.php in your craft/config directory. As with any configuration option, this supports multi-environment options.
return array(
    '*' => array(
        // 'letter', 'legal', 'A4', etc.
        'pdfPaperSize' => 'letter',
        // 'portrait' or 'landscape'
        'pdfPaperOrientation' => 'portrait',
        // true|false
        'pdfAllowRemoteImages' => true,
    )
);
pdfPaperSize - handles the PDF paper size. You can find a full list of available sizes under Dompdf\Adapter\CPDF::$PAPER_SIZES (opens new window)pdfPaperOrientation - the PDF paper orientation, either portrait or landscapepdfAllowRemoteImages - option to enable/disable remote images in PDFs.