How to add the ability to zoom with two fingers?

Question

Android

How to add the ability to zoom with two fingers?
here is the screen, as you can see on the screen, the increase is possible only + and -:

the schedule is loaded through the code:

//---you need this to prevent the webview from
// launching another browser when a url
// redirection occurs-—
        webView.setWebViewClient(new Callback());

        String pdfURL = "http://www.1kurs.pdf";
        webView.loadUrl(
                "http://docs.google.com/gview?embedded=true&url=" + pdfURL);

        setContentView(webView);
    }

Answer 1

mWebView.getSettings().setSupportZoom(true);