// For complete examples and data files, please go to https://github.com/aspose-words/Aspose.Words-for-.NET.git.
Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);
            
builder.StartBookmark("MyBookmark");
builder.Writeln("Text inside a bookmark.");
builder.EndBookmark("MyBookmark");

// Retrieve a list of all custom document properties from the file.
CustomDocumentProperties customProperties = doc.CustomDocumentProperties;
// Add linked to content property.
DocumentProperty customProperty = customProperties.AddLinkToContent("Bookmark", "MyBookmark");
customProperty = customProperties["Bookmark"];

bool isLinkedToContent = customProperty.IsLinkToContent;
string linkSource = customProperty.LinkSource;
string customPropertyValue = customProperty.Value.ToString();