下载和运行.apk文件时发生解析错误

我的应用程序中有一个功能，允许用户下载新版本。
但是我的问题是，当我启动应该启动安装过程的意图时，出现一条消息：

解析错误。解析软件包时出现问题

这是我的代码

Button button;
String urlApp = "example.com/app.apk"
String fileName = "app.apk";
DownloadManager downloadManager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    button = (Button) findViewById(R.id.button);

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            File file = new File(Environment.DIRECTORY_DOWNLOADS, fileName);
            if (file.exists()){
                boolean deleted = file.delete();
                Toast.makeText(getApplicationContext(), "Deleted", Toast.LENGTH_SHORT).show();
            }

            downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(urlApp));
            request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, fileName);
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            request.setTitle("Click to update");
            downloadManager.enqueue(request);
            registerReceiver(onComplete, new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));

        }
    });

}

private void openFile() {
    Intent install = new Intent(Intent.ACTION_VIEW);
    install.setDataAndType(Uri.fromFile(new File(Environment.DIRECTORY_DOWNLOADS+"/"+fileName)),
            "application/vnd.android.package-archive");
    startActivity(install);
}

BroadcastReceiver onComplete = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        openFile();
    }
};

}

仅适用于.apk文件，.txt文件可以正常工作。logcat上没有错误。删除也不起作用，但这不是我的主要问题。

提前致谢

抱歉，这是一个愚蠢的问题，但这是我第一次与下载管理器合作