Great question. Right now Unbounce’s native forms do not have a feature built into them to support a file upload (it’s just not something that is built into them right now - plus we don’t have a dedicated storage space for the files your potential leads would be uploading) however this can definitely be accomplished using a third party form.
Formstack, Wufoo, and Jotform are all strong picks that we see Unbounce customers experiment with time to time. So you could build the body of your landing page with Unbounce and then manage your lead data (with their file uploads) in the form tool you decide to use.
With that said, this is something we’re hoping to implement into Unbounce’s native forms soon! Perhaps some of the other folks in the community will have some other ideas you can try too.