PDF.js 预览添加水印

效果图：

简书

只需要在 viewer.js 和 viewer.css 里面修改即可

viewer.js (约7180行)：

                    var _this = this;                    if (this.renderingState !== _pdf_rendering_queue.RenderingStates.INITIAL) {                        console.error('Must be in new state before drawing');                        this.reset();
                    }                    if (!this.pdfPage) {                        this.renderingState = _pdf_rendering_queue.RenderingStates.FINISHED;                        return Promise.reject(new Error('Page is not loaded'));
                    }                    this.renderingState = _pdf_rendering_queue.RenderingStates.RUNNING;                    var pdfPage = this.pdfPage;                    var div = this.div;                    var canvasWrapper = document.createElement('div');
                    canvasWrapper.style.width = div.style.width;
                    canvasWrapper.style.height = div.style.height;
                    canvasWrapper.classList.add('canvasWrapper');                    if (this.annotationLayer && this.annotationLayer.div) {
                        div.insertBefore(canvasWrapper, this.annotationLayer.div);
                    } else {
                        div.appendChild(canvasWrapper);
                    }                    var textLayer = null;                    if (this.textLayerFactory) {                        var textLayerDiv = document.createElement('div');
                        textLayerDiv.className = 'textLayer';
                        textLayerDiv.style.width = canvasWrapper.style.width;
                        textLayerDiv.style.height = canvasWrapper.style.height;   //从这里开始
                        var cover = document.createElement('div');
                        cover.className = "cover";                        var defaultSettings = {                            watermark_txt: "简书",                            watermark_x: 0,//水印起始位置x轴坐标
                            watermark_y: 0,//水印起始位置Y轴坐标
                            watermark_rows: 30,//水印行数
                            watermark_cols: 100,//水印列数
                            watermark_x_space: 10,//水印x轴间隔
                            watermark_y_space: 10,//水印y轴间隔
                            watermark_color: 'red',//水印字体颜色
                            watermark_alpha: 0.3,//水印透明度
                            watermark_fontsize: '20px',//水印字体大小
                            watermark_font: '微软雅黑',//水印字体
                            watermark_width: 120,//水印宽度
                            watermark_height: 80,//水印长度
                            watermark_angle: 45//水印倾斜度数
                        };                        var oTemp = document.createDocumentFragment();                        //获取页面最大宽度
                        var page_width = Math.max(document.body.scrollWidth, document.body.clientWidth);                        //获取页面最大长度
                        var page_height = Math.max(document.body.scrollHeight, document.body.clientHeight);                        //如果将水印列数设置为0，或水印列数设置过大，超过页面最大宽度，则重新计算水印列数和水印x轴间隔
                        if (defaultSettings.watermark_cols == 0 || (parseInt(defaultSettings.watermark_x + defaultSettings.watermark_width * defaultSettings.watermark_cols + defaultSettings.watermark_x_space * (defaultSettings.watermark_cols - 1)) > page_width)) {
                            defaultSettings.watermark_cols = parseInt((page_width - defaultSettings.watermark_x + defaultSettings.watermark_x_space) / (defaultSettings.watermark_width + defaultSettings.watermark_x_space));
                            defaultSettings.watermark_x_space = parseInt((page_width - defaultSettings.watermark_x - defaultSettings.watermark_width * defaultSettings.watermark_cols) / (defaultSettings.watermark_cols - 1));
                        }                        //如果将水印行数设置为0，或水印行数设置过大，超过页面最大长度，则重新计算水印行数和水印y轴间隔
                        if (defaultSettings.watermark_rows == 0 || (parseInt(defaultSettings.watermark_y + defaultSettings.watermark_height * defaultSettings.watermark_rows + defaultSettings.watermark_y_space * (defaultSettings.watermark_rows - 1)) > page_height)) {
                            defaultSettings.watermark_rows = parseInt((defaultSettings.watermark_y_space + page_height - defaultSettings.watermark_y) / (defaultSettings.watermark_height + defaultSettings.watermark_y_space));
                            defaultSettings.watermark_y_space = parseInt(((page_height - defaultSettings.watermark_y) - defaultSettings.watermark_height * defaultSettings.watermark_rows) / (defaultSettings.watermark_rows - 1));
                        }                        var x;                        var y;                        for (var i = 0; i < defaultSettings.watermark_rows; i++) {
                            y = defaultSettings.watermark_y + (defaultSettings.watermark_y_space + defaultSettings.watermark_height) * i;                            for (var j = 0; j < defaultSettings.watermark_cols; j++) {
                                x = defaultSettings.watermark_x + (defaultSettings.watermark_width + defaultSettings.watermark_x_space) * j;                                var mask_div = document.createElement('div');
                                mask_div.id = 'mask_div' + i + j;
                                mask_div.className = 'mask_div';
                                mask_div.appendChild(document.createTextNode(defaultSettings.watermark_txt));                                //设置水印div倾斜显示
                                mask_div.style.webkitTransform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                                mask_div.style.MozTransform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                                mask_div.style.msTransform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                                mask_div.style.OTransform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                                mask_div.style.transform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                                mask_div.style.visibility = "";
                                mask_div.style.position = "absolute";                                //奇偶行错开，这样水印就不对齐，显的不呆板
                                if (i % 2 != 0) {
                                    mask_div.style.left = x + 100 + 'px';
                                } else {
                                    mask_div.style.left = x + 'px';
                                }
                                mask_div.style.top = y + 'px';
                                mask_div.style.overflow = "hidden";
                                mask_div.style.opacity = defaultSettings.watermark_alpha;
                                mask_div.style.fontSize = defaultSettings.watermark_fontsize;
                                mask_div.style.fontFamily = defaultSettings.watermark_font;
                                mask_div.style.color = defaultSettings.watermark_color;
                                mask_div.style.textAlign = "center";
                                mask_div.style.width = canvasWrapper.style.width + 'px';
                                mask_div.style.height = canvasWrapper.style.height + 'px';
                                mask_div.style.display = "block";
                                oTemp.appendChild(mask_div);
                            }
                        }
                        cover.appendChild(oTemp);//这里结束
                        if (this.annotationLayer && this.annotationLayer.div) {
                            div.insertBefore(textLayerDiv, this.annotationLayer.div);//不要忘记这里
                            div.appendChild(cover);

                        } else {
                            div.appendChild(textLayerDiv);//还有这里
                            div.appendChild(cover);
                        }
                        textLayer = this.textLayerFactory.createTextLayerBuilder(textLayerDiv, this.id - 1, this.viewport, this.enhanceTextSelection);//这里。。
                        var cover = document.getElementsByClassName('cover');                        for (var i = 0, len = cover.length; i < len; i++) {
                            cover[i].style.width = canvasWrapper.style.width;
                            cover[i].style.height = canvasWrapper.style.height;
                        }
                    }                    this.textLayer = textLayer;                    var renderContinueCallback = null;``

作者：H_婷
链接：https://www.jianshu.com/p/9f349e41a7b2