<Window x:Class="WpfApp39.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp39"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid ShowGridLines="True">
            <Grid.ColumnDefinitions>
                <ColumnDefinition/><ColumnDefinition/><ColumnDefinition/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition/><RowDefinition/><RowDefinition/>
            </Grid.RowDefinitions>

            <!-- このGridを回転させる -->
            <Grid x:Name="MyGrid" Grid.Row="1" Grid.Column="1" Background="Pink" RenderTransformOrigin="0.5,0.5"
                  IsManipulationEnabled="True"
                  ManipulationDelta="Grid_ManipulationDelta">

                <TextBlock Text="あ" HorizontalAlignment="Center" VerticalAlignment="Center" FontSize="50"/>
            </Grid>
        </Grid>
    </Grid>
</Window>

using System.Windows;
using System.Windows.Input;
using System.Windows.Media;

namespace WpfApp39
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Grid_ManipulationDelta(object sender, ManipulationDeltaEventArgs e)
        {
            var delta = e.DeltaManipulation;
            Matrix matrix = (MyGrid.RenderTransform as MatrixTransform).Matrix;
            matrix.Translate(delta.Translation.X, delta.Translation.Y);// 指の移動量を指定して対象を移動

            var scaleDelta = delta.Scale.X;//上下と左右に同じ量拡大するときは、Xの拡大率だけとればOK
            var orgX = e.ManipulationOrigin.X;//指の中心点(X)
            var orgY = e.ManipulationOrigin.Y;//指の中心点(Y)
            matrix.ScaleAt(scaleDelta, scaleDelta, orgX, orgY);//中心を指定して対象を拡大
            MyGrid.RenderTransform = new MatrixTransform(matrix);
        }
    }
}