Here is what i recommend
Put the file behind a pass protected directory.
Make the surfer sign up to what ever it is and click the confirm link to get the pass word.
Usually when the click the link they go to a page saying
"Thank you for verifying your email to blah blah blah.
Tell them that that they have to do all that to get the pass which will be the word that comes 4th for examples
Thank you for _____
The blank is the password which is verifying.
