Download PDF Files in Android WebView

Question

I am using webview for showing my website to my users. The user needs to login to access files from my websites. Most of the files are in pdf format. But I noticed that the files not downloading properly and the files downloaded are just in html format and it only contain a error 44 error Page not found. After I googled about this problem I found that it may happening because the app doesn't in login state while downloading. I am new to android development so I request for a clear answer if possible for my understanding. Please check my code

webView.setDownloadListener(new DownloadListener() {


            @Override
            public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimetype, long contentLength){

                checkDownloadPermission();

                DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));

                request.setDescription("Download file...");
                request.setTitle(URLUtil.guessFileName(url, contentDisposition, mimetype));
                request.allowScanningByMediaScanner();
                request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED); //Notify client once download is completed!
                try {
                    request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, new URL(url).getFile());
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                }
                DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
                dm.enqueue(request);
                Toast.makeText(getApplicationContext(), "Downloading File", Toast.LENGTH_LONG).show();
            }
        });

    // This will handle downloading. It requires Gingerbread, though
        final DownloadManager manager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);

        // This is where downloaded files will be written, using the package name isn't required
        // but it's a good way to communicate who owns the directory
        final File destinationDir = new File (Environment.getExternalStorageDirectory(), getPackageName());

        if (!destinationDir.exists()) {
            destinationDir.mkdir(); // Don't forget to make the directory if it's not there
        }

@Override
            public boolean shouldOverrideUrlLoading(WebView view, String url) {


                webView.getSettings().setDomStorageEnabled(true);
                CookieManager.getInstance().acceptCookie();
                CookieManager.setAcceptFileSchemeCookies(true);
                webView.getSettings().setJavaScriptEnabled(true);

                boolean shouldOverride = false;
                // We only want to handle requests for mp3 files, everything else the webview
                // can handle normally
                if (url.endsWith(".pdf")) {
                    shouldOverride = true;
                    Uri source = Uri.parse(url);



                    // Make a new request pointing to the mp3 url
                    DownloadManager.Request request = new DownloadManager.Request(source);

                    String cookies = CookieManager.getInstance().getCookie(url);

                    request.addRequestHeader("cookie", cookies);


                    // Use the same file name for the destination
                    File destinationFile = new File (destinationDir, source.getLastPathSegment());
                    request.setDestinationUri(Uri.fromFile(destinationFile));
                    // Add it to the manager
                    manager.enqueue(request);
                }
                else
                    view.loadUrl(url);
                return shouldOverride;
            }