HarmonyOS 鸿蒙Next PDF文件读取内容为空（%PDF-1.5）

表现：下载的pdf文件读取内容只有一个’%PDF-1.5’；

具体代码：

dowLoadFile(data:DownloadParam,handler: CompleteHandler,preview: boolean){
data = JSON.parse(data+’’) as DownloadParam
let context = getContext(this) as common.UIAbilityContext;
let fileName = new Date().getTime()+getExtension(data.name)
let filesDir = context.filesDir;
let filePath = filesDir + ‘/’+fileName
try {
fs.accessSync(filePath);
fs.unlinkSync(filePath);
} catch (err) {
}
try {
this.loaded=false
request.downloadFile(context.getApplicationContext(), {
url: data.url,
filePath: filePath,
enableMetered:true
}).then((downloadTask: request.DownloadTask) => {
downloadTask.on(‘progress’, (receivedSize: number, totalSize: number)=>{
console.info(“downloadFile-receivedSize:” + receivedSize + " totalSize:" + totalSize);
});
downloadTask.on(‘complete’, async () => {
this.loaded=true
console.info(‘downloadFile-complete’);
let file = fs.openSync(filePath, fs.OpenMode.READ_WRITE);
let arrayBuffer = new ArrayBuffer(7424361);
let readLen = fs.readSync(file.fd, arrayBuffer);
let buf = buffer.from(arrayBuffer, 0, readLen);
console.info(downloadFile-file:${readLen}_${buf.toString()});
fs.closeSync(file);
const taskInfo = await downloadTask.getTaskInfo();
console.info(‘downloadFile-task-complete:’+status: ${taskInfo.status});
this.doPreview(fileName,filePath)
})
}).catch((err: BusinessError) => {
this.loaded=true
console.error(‘downloadFile-err-’,JSON.stringify(err));
});
} catch (error) {
let err: BusinessError = error as BusinessError;
console.error(Invoke downloadFile failed, code is ${err.code}, message is ${err.message});
} 

可以看到读取文件输出：

实际上的文件有7M：

；；；；；；下载图片之内的资源则不会出现这种情况。

顺便请教一下大家，我希望下载文件，保存到文件系统中，可以通过我的文件查找到应该怎么操作呢；下载下来后选择打开方式打开有有什么API可以实现了