当在Android应用程序中使用DownloadManager下载PDF文件时，可能会出现问题。具体来说，如果下载的文件格式为PDF且使用基本的Android下载监听器，该文件可能无法从本地存储中读取。

为了解决此问题，我们可以将PDF文件的MIME类型与下载监听器相关联。以下是一个示例：

DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
String url = "https://example.com/sample.pdf";
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
request.setDescription("Downloading PDF file");  
request.setTitle("Sample.pdf");
request.setMimeType("application/pdf"); // 设置 MIME类型

// 在下载完成后打开文件
File file = new File(Environment.getExternalStorageDirectory().getPath() + "/Download/Sample.pdf");
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
intent.setDataAndType(Uri.fromFile(file), "application/pdf");
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "Sample.pdf");
request.setMimeType("application/pdf");
request.setVisibleInDownloadsUi(true);
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "Sample.pdf");
request.allowScanningByMediaScanner();
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
request.setMimeType("application/pdf");
request.allowScanningByMediaScanner();

long downloadId = dm.enqueue(request);

使用以上代码示例，我们可以成功下载PDF文件并确保它可以从本地存储中读取。