File Upload & Render in Checkbox

I am trying to use Contact Form 7 to allow visitors to upload a file, which would then appear in a textarea.

This page explains what I am trying to achieve;

http://learn-english.nz/file-upload

Can anybody help to figure this out please?

thanks in advance.

DbO