I'll admit to a personal bias here - I don't like these type of scripts, they cause far to much trouble. The problem can be two fold.
Firstly, it's a form for someone to put an email addresss in and send an email to a different address, so it has the potential to be used for spamming (especially if you allow the person hitting the site to be able to add any text to the email going out).
Secondly, if it's an autoresponder on an email account - then what happened when there is some incoming spam from a spoofed email address. The scripts sends your email out to that email address (which wasn't asked for ... and hence technically is spam) and you turn into a spammer.
I would primarily suggest a simple link to the PDF file, that they can download it - rather than sending any email.
If they want to do it with an email script from a web page, then I'd use a captcha code as minimum, to try and prevent bots from using the script.
Having said that, if you want to do it via a script, have you had a look at hotscripts.com ?
