uniapp保存打开文件并修改文件名

async openPdf() {
        const {data: result} = await uni.$http.get('/api/user/add_pdf', {id: this.enrollId})
        if (result.state == 1) {
         // 此为文件名称，名称前需带/,如(/文档.pdf)
          let fileName = result.url.slice(4)
          	wx.downloadFile({
          		url: this.baseUrl + result.url,
          		filePath: wx.env.USER_DATA_PATH + fileName,
          		success(res) {
          			const filePath = res.filePath || res.tempFilePath
                //下载完成自动打开文件
          			wx.openDocument({
          				showMenu: true,
          				filePath,  
          				fileType: 'pdf',
          				success: function (res) {
          					console.log('打开文档成功') 
          				}
          			})
          		},
          		fail(err) {
          			console.log('打开文档失败', err)
          		}
          	}) 
          }