public CIMFill ConstructPictureFill( 
   string fileName,
   double size
)

/// <summary>
/// Constructs a picture fill with the specified parameters.
/// ![ConstructPictureFill](https://ArcGIS.github.io/arcgis-pro-sdk/images/Symbology/ConstructPictureFill.png)
/// </summary>
{
  //Note: Run withing QueuedTask
  CIMStroke outline = SymbolFactory.Instance.ConstructStroke(CIMColor.CreateRGBColor(110, 110, 110), 2.0, SimpleLineStyle.Solid);
  //picture
  var imgPath = Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), @"Images\CaliforniaEmblem.png");
  var pictureFill = SymbolFactory.Instance.ConstructPictureFill(imgPath, 64);

  List<CIMSymbolLayer> symbolLayers = new()
  {
    outline,
    pictureFill
  };
  CIMPolygonSymbol pictureFillPolygonSymbol = new CIMPolygonSymbol() { SymbolLayers = symbolLayers.ToArray() };
  //To apply the symbol to a polygon feature layer
  //var renderer = theLayer.GetRenderer() as CIMSimpleRenderer;
  //renderer.Symbol = pictureFillPolygonSymbol.MakeSymbolReference();
  //theLayer.SetRenderer(renderer);
}