首先确保安装了mpdf扩展 composer require mpdf/mpdf

public function createWaterPdf($file_path,$water_text){date_default_timezone_set('PRC');ini_set('memory_limit', '6400M');ini_set('max_execution_time', '0');try{$mpdf = new Mpdf();$pageCount   = $mpdf->SetSourceFile($file_path); //读取原始文件页数$tplId       = $mpdf->ImportPage(1); //获取第一张信息$size        = $mpdf->getTemplateSize($tplId);$orientation = $size['orientation'] ?? 'P';//创建缓存文件夹$cachePath = Yii::$app->basePath.'/runtime/pdfwater';if (!is_dir($cachePath)) {mkdir($cachePath, 0777, true);}//第一步：创建水印背景图片$width  = ceil($size['width'] / 25.4 * 300); //换算成300分辨率对应的尺寸大小$height = ceil($size['height'] / 25.4 * 300);$image  = imagecreate($width, $height);$bg     = imagecolorallocate($image, 255, 255, 255);imagefill($image, 0, 0, $bg);imagepng($image,$cachePath.'/background.png');imagedestroy($image);//第二步：创建水印图片$image  = $cachePath . '/background.png';$info   = getimagesize($image);$imgExt = image_type_to_extension($info[2], false);  //获取文件后缀$fun = "imagecreatefrom{$imgExt}";$imgInfo = $fun($image);$fontFile  = Yii::$app->params['fontPath'] . '/simhei.ttf'; //字体文件名，必须要，需要下载对应的字体文件，放到指定的目录$fontSize  = 70; //字体尺寸$fontColor = ImageColorAllocate($imgInfo,0,0,0); //字体颜色，这里是黑色$textAngle = 30; //文字显示的角度，0表示水平显示$x_length = $info[0];$y_length = $info[1];$text_length = (mb_strlen($water_text) + 3)*0.833*70;//判断用多大的纸张if ($orientation == 'P') {$water_h = ceil($x_length/3)-100;$page_width = $size[0];$page_height = $size[1];} else {$water_h = ceil($y_length/3)-100;$page_width = $size[1];$page_height = $size[0];}if ($page_width > 900 || $page_width < 150 || $page_height > 1200 || $page_height < 150) return ['code'=>2,'msg'=>'文件尺寸不符合要求']; //此处不限制文件大小也行$water_w = $text_length * 1.732;if ($water_w < 1000) $water_w = 1000;//重复添加水印for ($x = 0; $x < $x_length; $x += $water_w) {for ($y = 0; $y < $y_length; $y += $water_h) {imagefttext($imgInfo,$fontSize,$textAngle,$x,$y,$fontColor,realpath($fontFile),$water_text); //把文字覆盖到图片上}}$quality = 100;if($imgExt == 'png') $quality = 9;//输出质量,JPEG格式(0-100),PNG格式(0-9)$getImgInfo = "image{$imgExt}";$getImgInfo($imgInfo, $cachePath.'/watermark.png', $quality);imagedestroy($imgInfo);//第三步：开始添加水印操作$arrPage = ['sheet-size' => [$page_width,$page_height], //指定纸张大小'orientation' => $orientation, //指定纸张方向];for($i=1; $i<=$pageCount; $i++){ //循环添加原始文件$mpdf->AddPageByArray($arrPage);$tplId = $mpdf->ImportPage($i);$mpdf->UseTemplate($tplId);//开始给pdf添加水印$mpdf->SetWatermarkImage($cachePath.'/watermark.png');$mpdf->showWatermarkImage = true;}$mpdf->Output($cachePath.'/watermask.pdf','F'); //新文件}catch (\Exception $e){return ['code'=>1,'msg'=>$e->getMessage()];}}