Относительный путь к файлу

            var directory = new Uri("file:///C:/Users/adm/Documents/Work/2017/Programming/INES%20v01/INES_Wpf%20v87/INES_Wpf_v01/INES_Wpf_v01/bin/Debug/INES-2008-R_web.pdf", UriKind.Absolute);
            WebBrowserINES.Navigate(directory);

        private string GetExeDirectory()
        {
            string codeBase = Assembly.GetExecutingAssembly().CodeBase;
            UriBuilder uri = new UriBuilder(codeBase);
            string path = Uri.UnescapeDataString(uri.Path);
            path = Path.GetDirectoryName(path);
            return path;
        }

            WebBrowserINES.Navigate(new Uri(System.IO.Path.Combine(GetExeDirectory(), "/INES-2008-R_web.pdf"), UriKind.Relative));

var uri2 = new System.Uri(path);
var converted = uri2.AbsoluteUri;

        private void Page_Loaded(object sender, RoutedEventArgs e)
        {
            WebBrowserINES.Navigate(new Uri(System.IO.Path.Combine(GetExeDirectory(), "/INES-2008-R_web.pdf"), UriKind.Absolute));
        }
 
        private string GetExeDirectory()
        {
            string codeBase = Assembly.GetExecutingAssembly().CodeBase;
            UriBuilder uri = new UriBuilder(codeBase);
            string path = Uri.UnescapeDataString(uri.Path);
            path = System.IO.Path.GetDirectoryName(path);
 
            var uri2 = new Uri(path);
            var converted = uri2.AbsoluteUri;
 
            return converted;
        }

    var dir = GetExeDirectory();
    var uri = new Uri(System.IO.Path.Combine(dir, "INES-2008-R_web.pdf"));
    //var uriAbs = uri.AbsoluteUri;
    WebBrowserINES.Navigate(uri);

static private string GetExeDirectory()
{
    string codeBase = Assembly.GetExecutingAssembly().CodeBase;
    UriBuilder uri = new UriBuilder(codeBase);
    string path = Uri.UnescapeDataString(uri.Path);
    path = System.IO.Path.GetDirectoryName(path);
    return path;
}