MainPage.xaml

<Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
    <ProgressBar Value="{Binding Progress}"
                 Minimum="0"
                 Maximum="1"
                 Visibility="{Binding Initialized, Converter={StaticResource InvertedBoolToVisibilityConverter}}"/>
    <TextBlock Text="{Binding Text}" 
               TextWrapping="Wrap"
               Visibility="{Binding Initialized, Converter={StaticResource BoolToVisibilityConverter}}"
               Style="{StaticResource BasicTextStyle}" />
</Grid>

ViewModel.cs

public ViewModel()
{
    var progress = new Progress<double>();
    progress.ProgressChanged += (s, v) => Progress = v;
    Init(progress);
}

private async void Init(IProgress<double> progress)
{
    var file = await Package.Current.InstalledLocation.GetFileAsync(@"Assets\Text.txt");
    Text = await FileIO.ReadTextAsync(file);
    for (int i = 0; i < 10; i++)
    {
        await Task.Delay(500);
        progress.Report((double)i/10);
    }
    Initialized = true;
}

public string Text
{
    get { return _text; }
    set
    {
        if (value == _text) return;
        _text = value;
        OnPropertyChanged();
    }
}

public double Progress
{
    get { return _progress; }
    set
    {
        if (value.Equals(_progress)) return;
        _progress = value;
        OnPropertyChanged();
    }
}

public bool Initialized
{
    get { return _initialized; }
    set
    {
        if (value.Equals(_initialized)) return;
        _initialized = value;
        OnPropertyChanged();
    }
}