Invoke PDF, Server returned HTTP response code: 400

Question

English is not my native language; please excuse typing errors.
Hope I improved the question.

1. I start a Script over Selenium, automated testing, WebDriver.
   
2. I perform a Link on HTML-Page
   
3. This link creates a new Browser Tab
   
4. This BrowserTab display a PDF/A Standard Document
   
5. I want to parse the PDF an verify its content
   
   

After HttpURLConnection I got Hypertext Transfer Protocol (HTTP) response status code: 400
and parsing the InputStream can not be done.
Over localhost it can be done.
Also I can hit link "curent URL" without any problems.
Selenium v2.45.0
Tested on IE 9 and Firefox 39.0.

How can I examine the problem?
I read about HTTP response code: 400
But didn't find solution for my problem
Could it be a redirect-problem?
Thank you
Here is my code:

public class httperrorStack {
public static void main ( String[] args )
{
    // Selnium WebDriver
    WebDriver driver = null;
    //driver = new FirefoxDriver();
    // Test with Browser IE 9 same Problem withFirefox 39.0
    System.setProperty("webdriver.ie.driver","C:\\dir\\IEDriverServer.exe");
    driver = new InternetExplorerDriver();

    String baseUrl = "http://##.###.###.##:#####/wps/portal"; //ATU2                
    // launch direct to Base URL
    driver.get(baseUrl);    
    // launch to Documentlink: opens PDF/A-Document in a new Browser Tab
    driver.findElement(By.xpath("//a[@title='document_link']")).click();    

    //Get all the window handles in a set
    Set <String> handles =driver.getWindowHandles();
    Iterator<String> it = handles.iterator();
    //iterate through windows
    while (it.hasNext()){
    String parent = it.next();
    String newwin = it.next();
    driver.switchTo().window(newwin);       

    URL url = null;
    try {
        // The CurrentURL of the documentlink
        // url = "http://##.###.###.###:#####/wps/myportal/dirname/dirname/dir-name/!dir/p/b1/about50characters/In"
        url = new URL(driver.getCurrentUrl());
    } catch (MalformedURLException e1) {            
        e1.printStackTrace();
    }                

    // verify connection
    HttpURLConnection connection = null;
    HttpURLConnection httpConn = (HttpURLConnection)connection;
    try {
        httpConn = (HttpURLConnection)url.openConnection();
    } catch (IOException e1) {            
        e1.printStackTrace();
    }
    InputStream is = null;

    // Response Code = 400
    try {
        if (httpConn.getResponseCode() >= 400) {
            is = httpConn.getErrorStream();
            // httpConn.getResponseCode() = 400
            //httpConn.getErrorStream() = "sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@1d082e88"
        } else {
            is = httpConn.getInputStream();
        }
    } catch (IOException e1) {
            e1.printStackTrace();
    }              

    try{            
        connection = (HttpURLConnection)url.openConnection();                    
        InputStream is2;
        if (connection.getResponseCode() >= 400) {
            is2 = connection.getErrorStream();
            //connection.getErrorStream() = "sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@60704c"                
        } else {
            is2 = connection.getInputStream();
        }                   


    }
    catch (Exception e){
        e.printStackTrace();
    }

    BufferedInputStream fileToParse = null;
    try {
        fileToParse = new BufferedInputStream(
                url.openStream());
    } catch (IOException e) {
        e.printStackTrace();
        // output of StackTrace
        /*java.io.IOException: Server returned HTTP response code: 400 for URL: http://##.###.###.##:#####/wps/redirect
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
        at java.net.URL.openStream(Unknown Source)
        at mypackage.httperrorStack.main(httperrorStack.java:134)*/
    }

    // Close Window
    driver.close();
    driver.switchTo().window(parent);
    driver.quit();  
    // exit the program explicitly
    System.exit(0);
      }
   }
}