//test
        $picConf = array();
        $picConf['image.']['file'] = t3lib_extMgm::extPath($this->extKey).'pi1/test1.pdf';
        if(!is_file($picConf['image.']['file'])){
            $picConf['image.']['file'] = "";
        }
        $theImgCode = '';
        if(is_file($picConf['image.']['file'])){
            $picConf['image.']['file.']['maxW'] = $this->conf['maxW'] ? $this->conf['maxW'] : 300;
            $picConf['image.']['file.']['maxH'] = $this->conf['maxH'] ? $this->conf['maxH'] : 600;
            $picConf['image.']['file.']['frame'] = 1;
            $picConf['image.']['altText'] = '';
            $picConf['image.']['titleText'] = '';
            $content .= $this->cObj->IMAGE($picConf['image.']);
        }

        //S1
        $document = new Imagick($picConf['image.']['file']);
        echo $document->getNumberImages();
        //S2
        $img_info = exec(t3lib_div::imageMagickCommand('identify', $cur_path));
        //echo .*\.pdf[3]

Or global: $GLOBALS[‘TYPO3_CONF_VARS’][‘GFX’][‘im_noFramePrepended’]