I really think you would be better off avoiding programming Outlook. It
appears you are going to need to do this once a day when you receive the
email. It is the receipt of the e-mail that will start the process. I would
suggest that you open  the attachment as normal (manually from Outlook) and
then run any further code from a macro stored in personal.xls (so that it is
available when you are looking at the opened attachment.

If you are determined to write code for the Outlook object model, I would
suggest posting your query on the Outlook VBA forum.