How can set Image and PDF size in UWP C#

Question

I am trying to generate a pdf in my project where I converted Image into Pdf and Image generated from Layout. Generated image size is very large and also There are not received good quality. Please Help me to solve this.

I am using this code in program.

 RenderTargetBitmap renderTargetBitmapimg = new RenderTargetBitmap();

            var mainlayoutHeight = pageStackPanel.ActualHeight;
            var mainlayoutWidth = pageStackPanel.ActualWidth;
            int mlHeight = Convert.ToInt32(mainlayoutHeight);
            int mlWidth = Convert.ToInt32(mainlayoutWidth);


            
            await renderTargetBitmapimg.RenderAsync(pageStackPanel, mlWidth, mlHeight);
            
            ///SAVE IMAGE IN FOLDER 
            var pixelBufferimg = await renderTargetBitmapimg.GetPixelsAsync();
            var pixels = pixelBufferimg.ToArray();
            var displayInformation = DisplayInformation.GetForCurrentView();
            var storageFolder = await KnownFolders.GetFolderForUserAsync(null, KnownFolderId.PicturesLibrary);

            StorageFolder projectFolder = await storageFolder.CreateFolderAsync("TestImage", CreationCollisionOption.OpenIfExists);
            var file = await projectFolder.CreateFileAsync(jpgFilename, CreationCollisionOption.GenerateUniqueName);

            using (var stream = await file.OpenAsync(FileAccessMode.ReadWrite))
            {
                var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, stream);
                encoder.SetPixelData(BitmapPixelFormat.Bgra8,
                                     BitmapAlphaMode.Premultiplied,
                                    (uint)renderTargetBitmapimg.PixelWidth,
                                    (uint)renderTargetBitmapimg.PixelHeight,
                                    200, 200,
                                    pixels);

                await encoder.FlushAsync();
                StorageFile prescriptionJpgFile = await projectFolder.GetFileAsync(jpgFilename);
                await stream.FlushAsync();
                stream.Seek(0);
                stream.Dispose();
                renderTargetBitmapimg = null;