Even if you use PDF format, you can't stop people from printing your content.
A person using [Alt]+[PrintScreen] can capture whats on their screen, paste into word and print. Although it will be an image and not text if the information is just research or reading then this method will work just fine.
I suggest you just show snippits of the file then allow access to the entire file only upon payment. Another way is to set up a subscription service via paypal and require a subscription before allowing people access to full file. This way you will receive some sort of payment from people who decide to view without payment. www.robertketter.com if you want more help. Robert Ketter