In order to write to the body of the message and include the signature, you need to program Outlook directly to create the message. I have added in the code from http://www.rondebruin.nl/win/s1/outlook/openclose.htm to open Outlook properly, and modified the code associated with the button to create the message, which should display the signature associated with the sending account.
The attachment path does not appear to represent a valid filename, in that there is no extension provided. You can add the extension to the code where the attachment is added. e.g.
.attachments.Add Cells(ActiveCell.Row, 10) & ".docx"
if the file is a document. If the file does not exist or the path is wrong, the code will not appreciate it. It would probably be wise to add code to validate whether the file exists at the named location before attempting to add it.