There are two answers to this question. 1) in some cases you can right click on the document that appears and from the contextual menu select the 'show as icon' option. This option doesn't always appear though. 2) even if you do this how the document appears to the receiver is determined more by the receiver's email software than how you send it. As far as I know, how you send the file (shown as document or icon) is respected only by Apple's email program - not other email programs.
There is a plugin available called Attachment Tamer that offers much more control over the way Mail deals with attachments. I started using it some years ago when PC-users would often complain that they either didn't receive my attachments or had other problems with them. Attachment Tamer solved the problem and also gave better control over whether attachments were sent as icons or inline graphics.
Usual caveat: I've no connection with Lokiware, just happy with their product.
I wish they did! It's strange, but most users don't seem to have problems with attachments, although some do.
As I said in my earlier post, I was constantly frustrated with many, but not all, of my recipients complaining that I'd forgot to send the attachment - which I obviously hadn't, even though I'd send them as icons, make them Windows-friendly, etc. Attachment Tamer immediately took away the agro .
Thank you for the credit.