I am afraid this is more complicated than one would think. First, you’d have to code the form yourself. Second, you’ll need some server side scripting to support it.
And third… and this is the biggie, if you want anyone filling out a form to be able to do this (with no form of authorization), you’ll need a directory on the server with public write permission… something many ISP’s will give you grief over.
What I have done in the past is to create a landing page with a mailto link that instructs the user to send the file via email, or to use a service like FileStack.