I can think of two ways on which I would rather receive a document from a vendor, partner of client, instead of a .docx attachment or the like.
1. A link to an opengoo installation (or another Web system for which I have access) where I can view the document without having to have any particular application installed on my desktop or accessing device.
Client access could be read only, or restricted to commenting on the document.
2. The document embedded on the message so I can see it right away (again, without any particular application needed... only my e-mail client).
On a side note: I don't like receiving invoices.