for several reasons - the most important of which is that not everyone is going to have Microsoft Word installed on their computer. Some other Office suites will open Word docs, but may not deal with fields in the same way, so it's best not to do it that way.
The simplest way would be to have a web-form which can be filled in online and emailed to you from the server, but that wouldn't allow people to send you an image attachment.
Why don't you go that route anyway? get people to fill in an online form and include a field for their email address. Then you can send them an email in the normal way and ask them to send their image attachment in their reply.