how doI email back an attachment once I have added my comments
Save it to your hard drive and attach it to an email?
Not even sure what product you are referring to so that's about all I can suggest.
Assuming that you have received a PDF as an email attachment, want to add comments, then return the document?
Never modify the attachment directly; always save it first to your local disk, modify it, then send it back the way ~graffiti suggested.