Csharp 添加的水印中的符号在 C# Word 互操作中未正确显示

我的程序有一个向Word文件添加水印的功能，但符号‘C’没有正确显示，只是像附件一样是一个正方形.(它是旋转的).

我想我必须编写一行代码才能使用这些符号，但我找不到它.有人能帮帮我吗？

if (file.Watermark == true)
                    {
                        Microsoft.Office.Interop.Word.Shape wordShape = null;
                        foreach (Microsoft.Office.Interop.Word.Section section in wordDoc.Sections)
                        {
                            wordShape = section.Headers[Microsoft.Office.Interop.Word.WdHeaderFooterIndex.wdHeaderFooterPrimary].Shapes.AddTextEffect(
                                             Microsoft.Office.Core.MsoPresetTextEffect.msoTextEffect1,
                                             "Ⓒ gg", "Arial", (float)30,
                                             Microsoft.Office.Core.MsoTriState.msoTrue,
                                             Microsoft.Office.Core.MsoTriState.msoFalse,
                                             150, 150, ref o);
                            wordShape.Fill.Visible = Microsoft.Office.Core.MsoTriState.msoTrue;
                            wordShape.Fill.Solid();
                            wordShape.Fill.ForeColor.RGB = (Int32)Microsoft.Office.Interop.Word.WdColor.wdColorGray15;
                            wordShape.Line.Visible = Microsoft.Office.Core.MsoTriState.msoFalse;
                            wordShape.RelativeHorizontalPosition = Microsoft.Office.Interop.Word.WdRelativeHorizontalPosition.wdRelativeHorizontalPositionMargin;
                            wordShape.RelativeVerticalPosition = Microsoft.Office.Interop.Word.WdRelativeVerticalPosition.wdRelativeVerticalPositionMargin;
                            wordShape.Left = 20;
                            wordShape.Top = 250;
                            wordShape.Rotation = -45;
                        }
                    }