Tips:大概率问题是域名没配正确，下载的文件地址错了

 pdfclick(link) {
     var link= http://cdn.ylnhome.com/shangcheng/168489780904143.pdf 
      if (link.indexOf('https') == -1) {
            link = item.link.replace('http', 'https')
        }
//http转https
      console.log(link, 'link')
      wx.downloadFile({
        url: link,
        success: function(res) {
          console.log(res, 'success')
          var Path = res.tempFilePath //返回的文件临时地址，用于后面打开本地预览所用
          wx.openDocument({
            filePath: Path,
            success: function(res) {},
          })//直接打开
        },
        fail: function(res) {
          console.log(res, 'fail')
        },
      })
    },

 域名配置如下