public override byte[] ToEsriShape()

{
  // create an envelope
  List<MapPoint> coordsZM = new List<MapPoint>
{
  MapPointBuilderEx.CreateMapPoint(1001, 1002, 1003, 1004),
  MapPointBuilderEx.CreateMapPoint(2001, 2002, Double.NaN, 2004),
  MapPointBuilderEx.CreateMapPoint(3001, -3002, 3003, 3004),
  MapPointBuilderEx.CreateMapPoint(1001, -4002, 4003, 4004)
};

  Envelope envelope = EnvelopeBuilderEx.CreateEnvelope(
             coordsZM[0], coordsZM[2], SpatialReferences.WGS84);

  // export and import
  EsriShapeExportFlags exportFlags = EsriShapeExportFlags.EsriShapeExportDefaults;
  EsriShapeImportFlags importFlags = EsriShapeImportFlags.EsriShapeImportDefaults;
  byte[] buffer = GeometryEngine.Instance.ExportToEsriShape(exportFlags, envelope);
  Polygon importedPolygon = GeometryEngine.Instance.ImportFromEsriShape(
                 importFlags, buffer, envelope.SpatialReference) as Polygon;
  Envelope importedEnvelope = importedPolygon.Extent;

  // export without z,m
  buffer = GeometryEngine.Instance.ExportToEsriShape(
          EsriShapeExportFlags.EsriShapeExportStripZs |
          EsriShapeExportFlags.EsriShapeExportStripMs, envelope);
  importedPolygon = GeometryEngine.Instance.ImportFromEsriShape(
          importFlags, buffer, SpatialReferences.WGS84) as Polygon;
  importedEnvelope = importedPolygon.Extent;

  bool hasZ = importedEnvelope.HasZ;      // hasZ = false
  bool hasM = importedEnvelope.HasM;      // hasM = false

  // export with shapeSize
  int bufferSize = GeometryEngine.Instance.GetEsriShapeSize(
                                         exportFlags, envelope);
  buffer = new byte[bufferSize];

  bufferSize = GeometryEngine.Instance.ExportToEsriShape(
                               exportFlags, envelope, ref buffer);
  importedPolygon = GeometryEngine.Instance.ImportFromEsriShape(
                      importFlags, buffer, envelope.SpatialReference) as Polygon;
  importedEnvelope = importedPolygon.Extent;

  // or use the envelope and envelopeBuilderEx classes
  buffer = envelope.ToEsriShape();
  // buffer represents a polygon as there is not an envelope Esri shape buffer
  // EnvelopeBuilderEx.FromEsriShape takes a polygon Esri shape buffer and returns the extent of the polygon.
  importedEnvelope = EnvelopeBuilderEx.FromEsriShape(buffer);
}