check out this https://smartforms.business.gov.au/eForms03/getForm?formName=ipaustralia.gov.au-trademark-registration-renewal-fee-payment-v2-1.pdf though im not sure how you could really secure it in the way that you want without them being on the web anyway. like, how would the pdf/exe know that their emails were valid? how would the emails get sent back to you? it seems like it would be hard to not get branded as spyware if your file is sending data back to somewhere. perhaps it would be better to leave it on the web via secure access, using a standard script to send a validation email back to them, which they would have to reply to to gain access. if they have to do all that in a "document", it doesnt seem like that much of an advantage to be a document at all, rather than just web pages. the site could be configured to only accept logins from say three different IPs in a week, which would stop people sharing the url/login/password combination. but they could still copy and paste the text from their browsers, or save the page HTML. your idea would be pretty cool if there was an easy enough way to do it. ( i am planning to release some material myself as PDF so i am interested in this too).
It seems that perhaps the only very easy way to do it is with the software expressly designed for the purpose and in widespread usage. The one I've come across, that's been recommended to me (and I don't mean by affiliates with an incentive to sell it), is called "e-book Pro 6.0". But this is ".exe" software, not for PDF's. The sales-page, if you want to see it, is here (and obviously that's not an affiliate link and I have no connection at all with it, except that I'll probably become a customer if I can't find an easy way to do what I want with a PDF).
It might be worth a look, especially if your niche is full of people who wont care what format it is in, even an .exe (and dont have many mac users, presumably it wont work on a mac??). Have you heard about anyone else (i mean in real life, not from the tesimonials on an ad) that has done well with that type of product?
All this password stuff IMO just puts out the message "I dont trust you guys". So you want to give away an ebook ? What I do is have 2 products, somehow make the 1 much better than the other. So you capture their email and you send them the link for the free report. In the link that has the report (right at the bottom) have the top bit say something like. "Before you download your free ebook, how would you like to get your hands on XZY ebook ? All you have to do is tell 3 friends (via tell a friend script) which will then give them the download link for the 2nd ebook. And then it works virally in theory.
Clever idea. I think the way forward is simply to make the most of the situation rather than trying to fight it. You won't be able to stop people sharing. So think of ways in which you can use this to increase your marketing and drive traffic where you want it.