Documents.Open method: Problem with optional parameters

Hi
I want to open a word document, using .NET variables. Documentation for the command is here:
https://msdn.microsoft.com/de-de/library/microsoft.office.interop.word.documents.open(v=office.11).aspx

Document Open(
	[In] ref object FileName, 
	[In, Optional] ref object ConfirmConversions, 
	[In, Optional] ref object ReadOnly, 
	[In, Optional] ref object AddToRecentFiles, 
	[In, Optional] ref object PasswordDocument, 
	[In, Optional] ref object PasswordTemplate, 
	[In, Optional] ref object Revert, 
	[In, Optional] ref object WritePasswordDocument, 
	[In, Optional] ref object WritePasswordTemplate, 
	[In, Optional] ref object Format, 
	[In, Optional] ref object Encoding, 
	[In, Optional] ref object Visible, 
	[In, Optional] ref object OpenAndRepair, 
	[In, Optional] ref object DocumentDirection, 
	[In, Optional] ref object NoEncodingDialog, 
	[In, Optional] ref object XMLTransform
);

As you can see there, the command has a lot of optional parameters. The parameters are all of type "Object".
Has somebody an idea how to use such a function from C/AL without using all parameters or how to use placeholders?

Thx in advance
Thomas