public string HelpTopicUrl { get; set; }

Public Property HelpTopicUrl As String
	Get
	Set

public:
property String^ HelpTopicUrl {
	String^ get ();
	void set (String^ value);
}

Applies only to objects of type ContextualHelpType.ChmFile. If empty or nullNothingnullptra null reference (Nothing in Visual Basic), the default page of the help file will be displayed.
Obtain the URL by:

1. Open the chm file and go to the page you want to show.
2. Right click on the page, and choose the Properties command.
3. In the middle of properties page there is a property called: Address (URL). The end of the URL contains the topic URL used to open the help file to the correct page. Here is an example: mk:@MSITStore:C:\RevitAPI2013.chm::/WhatsNew.htm The help topic URL of this page is "WhatsNew.htm". Another example: mk:@MSITStore:C:\RevitAPI2013.chm::/html/329b02eb-5ee4-1715-2fbf-2cbbc0d3ff2a.htm The help topic URL of this page is "html/329b02eb-5ee4-1715-2fbf-2cbbc0d3ff2a.htm".