PDF file download problem with android downloadlisteners

I can Download all by adding following code in my webview android App. But I can't download pdf file specially from http://www.garmentsmis.com/Efficiency_Calculator.aspx. When i click download it crash App.

//Runtime External storage permission for saving download files
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M) {
            if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE)
                    == PackageManager.PERMISSION_DENIED) {
                Log.d("permission", "permission denied to WRITE_EXTERNAL_STORAGE - requesting it");
                String[] permissions = {Manifest.permission.WRITE_EXTERNAL_STORAGE};
                requestPermissions(permissions, 1);
            }
        }




        //handle downloading
        web_view.setDownloadListener(new DownloadListener()
        {
            @Override
            public void onDownloadStart(String url, String userAgent,
                                        String contentDisposition, String mimeType,
                                        long contentLength) {
                DownloadManager.Request request = new DownloadManager.Request(
                        Uri.parse(url));
                request.setMimeType(mimeType);
                String cookies = CookieManager.getInstance().getCookie(url);
                request.addRequestHeader("cookie", cookies);
                request.addRequestHeader("User-Agent", userAgent);
                request.setDescription("Downloading File...");
                request.setTitle(URLUtil.guessFileName(url, contentDisposition, mimeType));
                request.allowScanningByMediaScanner();
                request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
                request.setDestinationInExternalPublicDir(
                        Environment.DIRECTORY_DOWNLOADS, URLUtil.guessFileName(
                                url, contentDisposition, mimeType));
                DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
                dm.enqueue(request);
                Toast.makeText(getApplicationContext(), "Downloading File. Go to Download folder from File Manager.", Toast.LENGTH_LONG).show();
            }});

Can anybody explaine me what i need to do? Thanks.