I want to put some codes into the clipboard, but it always fails. The code is as follows
When I switch from another phrase to this one, it will look like this

Any suggestions are welcome. Thanks in advance
___________________________________________________________________
class Program
{
static void Main()
{
DocumentModel document = new DocumentModel();
Section section = new Section(document);
document.Sections.Add(section);
Paragraph paragraph = new Paragraph(document);
section.Blocks.Add(paragraph);
Run run = new Run(document, "Hello World!");
paragraph.Inlines.Add(run);
}
}
___________________________________________________________________