The simplest method of cleaning bookmark content is setting Bookmark.Text property to an empty string.
However, that will work only for the simplest of bookmarks. For bookmark spanning multiple nodes with mixed content, like several paragraphs and tables, it can fail with "Start and end node should have the same grand parent" exception.
So if your bookmark is simple, then just set its Text property to an empty string. If it is not - use workaround code provided in the following Aspose.Words blog article:
http://www.aspose.com/COMMUNITY/blogs/aspose.words/archive/2007/03/13/70192.aspx
Vladimir Averkin
Developer/Technical Support
Aspose Auckland Team