不调用其他库读取pdf文档页数

    wx.chooseMessageFile({
      count: 1,
      type: 'file',
      success(res) {
        const tempFilePaths = res.tempFiles
        
        //调用getFileSystemManager
        const fs = wx.getFileSystemManager()
        fs.readFile({
          filePath: tempFilePaths[0].path,
          encoding: 'binary',
          position: 0,
          success(res) {
            console.log(res)
            //页数计算
              var count = res.data.match(/\/Type[\s]*\/Page[^s]/g).length;
              console.log('Number of Pages:', count);
          },
          fail(res) {
            console.error(res)
          }
        })
      }
    })