wx.downloadFile({                 // 示例 url，并非真实存在                 url: pdf_path,                 success(res) {                     const filePath = res.tempFilePath                     console.log(filePath)                     wx.openDocument({                         filePath,                         fileType:'pdf',                         success(res) {                             console.log('打开文档成功')                         }                     })                 }             }) wx.openDocument  用这个打开的文档，我在安卓机里再转发给好友，就打不开了，我看转发出去的没有文件后缀的，这里请优化下，分享出去带文件后缀，好打开文件