实现pdf预览主要有两种方式：
1、使用pdfjs已经写好的viewer.html页面。需要将pdfjs代码到服务器上，因为放到本地包有点大
2、将PDF文件渲染成Canvas

方案一 使用pdf.js时，需要传入文件路径，若我们拿到的文件是流那么需要先执行以下操作

var blob = new Blob([stream], {type: 'application/pdf'});
var fileOfBlob = new File([blob], fileName || new Date().getTime() + '.pdf');
var fileUrl = window.URL.createObjectURL(fileOfBlob );

打开方式

// waterMark  pdf水印
// file 打开的pdf 
window.open('/viewer.html?file=' + fileUrl + '&waterMark=' + '测试' + '&fileName=' + '测试');

方案二 vue工程中使用

// 安装
npm i pdfjs-dist
import PDFJS from 'pdfjs-dist'

template

<canvas v-for="item in totalPage" :key="item" :id='"the-canvas" + item' class="pdf-content"></canvas>

method

 let winW = document.documentElement.clientWidth
 let loadingTask = PDFJS.getDocument(this.pdfFile)
 loadingTask.promise.then(function (pdf) {
    let pageNum = pdf.numPages
    for (let i = 1; i <= pageNum; i++) {
      pdf.getPage(i).then(function (page) {
        let viewport = page.getViewport(1)
        let scale = (winW / viewport.width).toFixed(2)
        let scaledViewport = page.getViewport(scale)
        let canvas = document.getElementById('the-canvas' + i)
        let context = canvas.getContext('2d')
        canvas.height = scaledViewport.height
        canvas.width = scaledViewport.width
        let renderContext = {
          canvasContext: context,
          viewport: scaledViewport
        }
        let renderTask = page.render(renderContext)
        renderTask.then(function () {
        })
      })
    }
  }, function (reason) {
    console.error(reason)
  })