Outlook Form: Insert File is not available

[pho01]

I've created a custom Outlook form to send approval form out to the upper level management. the first page of the form includes a 'message' field. First time send the form out, the 'Insert File' button is enabled, but when a user received the form, the 'insert file' button is not visible on the form anymore. If for some reason user wants to edit the file attached and send it back to the sender, there's no way that they can do it. My question is:

- How do I enable this button so that when user receives it, this button is still available for use.
- If it can't be enabled, or visible for some reason, how do I create a command button on the form to allow user to do this?

Thanks much!