If someone sends you an email with a Word or Excel file attachment you're supposed to revise, first save the attachment to your computer before you begin editing it. Then — when you're finished editing it — attach the revised document to your email reply.
If you instead work directly on an attached e-mail file, chances are good the edits you made will be ignored, and when you reply all the person will see is the file as he or she first sent it to you.
Last week I asked someone to send me files as email attachments, and the 4 Publisher files turned a small 3KB message into 12MB.
Since large email attachments inflate the size of Outlook .pst files and can cause problems (as well as generating email quota warnings), I knew I needed to get those email attachments out of my mailbox.