Digital Signatures in Excel

Hi there,

I am currently using the Microsoft Office Primary Assemblies for
Office XP to write some code in .NET (C#) that allows me to
programatically open and sign an MS Office file (Word, Excel and
Powerpoint) and to verify if a file is signed or not.

I've been able to do it with MS Word documents (using
Microsoft.Office.Interop.Word namespace). I open the document, then
use wordDoc.Signatures.Add() to add a signature and
wordDoc.Signatures.Count to check for signatures.

However, I could not see if there's a similar way to do this in Excel.
I've been trying to look in the Microsoft.Office.Interop.Excel
namespace and haven't yet found a Signatures collection anywhere... In
Powerpoint, I noticed there's also a Signatures collection in the
Presentation class, but in Excel I did not see anything like that
anywhere.

Am I missing something ? Am I looking in the wrong places ? Is there a
way to programatically add a digital signature to a worksheet or
workbook in Excel ? Or it simply can't be done ?

Any help you can give would be greatly appreciated.

Thanks in advance,

Joao Maia