利用书签定位到Word文档的指定位置 (三种方法）
首先在Word文档中，设置书签，并命名(假设建了一个名为"BM_TEST"的书签）

然后使用C#操作Word

using MSWord = Microsoft.Office.Interop.Word;

private MSWord.Application wordApp;  //Word应用程序变量
private MSWord.Document wordDoc;     //Word文档变量
private Object Nothing = Missing.Value;
//初始化
wordApp = new MSWord.ApplicationClass();
wordDoc = wordApp.Documents.Add(ref Nothing, ref Nothing, ref Nothing, ref Nothing);
// 打开Word
object FileName = strPath;
object readOnly = false;
object isVisible = true;
wordDoc = wordApp.Documents.Open(ref FileName, ref Nothing, ref readOnly,
ref Nothing, ref Nothing, ref Nothing, ref Nothing, ref Nothing,
ref Nothing, ref Nothing, ref Nothing, ref isVisible, ref Nothing,
ref Nothing, ref Nothing, ref Nothing);

object bk = "BM_TEST";

方法一：使用Word应用程序变量，使用这种方法，wordApp.Documents.Open()中确保isVisible的值为true
if (wordApp.ActiveDocument.Bookmarks.Exists("BM_TEST"))
{
    wordApp.ActiveDocument.Bookmarks.get_Item(ref bk).Select();
    wordApp.Selection.TypeText("insert text");   // 插入文本
}

方法二：使用Word文档变量
if (wordDoc.Bookmarks.Exists("BM_TEST"))
{
    wordDoc.Bookmarks.get_Item(ref bk).Range.Text = "insert text"; // 插入文本
}

方法三：使用Goto函数，跳转到指定书签
object BookMarkName = "BM_TEST";
object what = MSWord.WdGoToItem.wdGoToBookmark;
wordDoc.ActiveWindow.Selection.GoTo(ref what, ref Nothing, ref Nothing, ref BookMarkName);
wordDoc.ActiveWindow.Selection.TypeText("Hello!");