This will work on c#.
        

            driver.FindElement(By.CssSelector("body")).SendKeys(OpenQA.Selenium.Keys.Control + "a");
            driver.FindElement(By.CssSelector("body")).SendKeys(OpenQA.Selenium.Keys.Control + "c");
            var txt = Clipboard.GetText();

I like this better then GetText(), because gettext returns all kinds of extra chars, this returns clean text.