webview will not load pdf files on link click

I have developed a web app that displays a list of pdf documents hosted on a web server. This app is embedded in a webview app for android however when I load the app on my phone, selection of a pdf link does nothing. What am I doing wrong? Thanks

Heres the java code:

package com.hellowebview;

import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class HellowebviewActivity extends Activity {
/** Called when the activity is first created. */

private WebView mWebView;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mWebView = (WebView) findViewById(R.id.webview);
    mWebView.getSettings().setJavaScriptEnabled(true);
    mWebView.loadUrl("http://aipnz.webs.com");
    mWebView.setWebViewClient(new HelloWebViewClient());
    mWebView.setScrollBarStyle(WebView.SCROLLBARS_OUTSIDE_OVERLAY);

}
private class HelloWebViewClient extends WebViewClient {
    @Override
    public boolean shouldOverrideUrlLoading(WebView webview, String url)
    {
        webview.loadUrl(url);
        return true;
    }
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event)
{
    if ((keyCode == KeyEvent.KEYCODE_BACK) && mWebView.canGoBack())
    {
        mWebView.goBack();
        return true;
    }
    return super.onKeyDown(keyCode, event);
}
}