如何在word文档中添加一个简单的短语

我用c#编程，我需要在每个ms-word文档的最后一页添加一个简单的短语。

i have try this

Word.Paragraph paragraph;
int totalPages;
Word.Range range;
range = doc.Content.Duplicate;
totalPages = range.ComputeStatistics(Word.WdStatistic.wdStatisticPages);
range = range.GoTo(Word.WdGoToItem.wdGoToPage, Type.Missing, totalPages, Type.Missing);
paragraph = doc.Paragraphs.Add(range);
paragraph.Range.Font.Name = "Arial";
paragraph.Range.Font.Size = 7;
paragraph.Alignment = Word.WdParagraphAlignment.wdAlignParagraphCenter;
paragraph.Range.Text = encrypt;

但是这个代码在最后一页添加了一个短语

doc.Content.InsertParagraphAfter();
Word.Paragraph paragraph = doc.Paragraphs(doc.Paragraphs.Count());
paragraph.Range.Font.Name = "Arial";
paragraph.Range.Font.Size = 7;
paragraph.Alignment = Word.WdParagraphAlignment.wdAlignParagraphCenter;
paragraph.Range.Text = encrypt;