A comment to this blog post at sans.org about secure file uploads suggests making a pre-formatted template available for users when they need to do file uploads. The user would use the template to add their own data and upload the resulting file. It suggests "encode the template in some way that an attacker would have a difficult time spoofing..."
This would supposedly help stop malicious files masquerading as the correct file types.
Would this work and how would one "encode" the template?