Unalterable 'read only' Document?

I am setting up a Business through a Website.
Without going into details (which I wouldn't anyway.....
), I need to send a Document to other people and I want that document to be able to be down-loaded, read and printed by the receiver, but they can't be able to alter it.
I know I can send a 'read only' Word Doc that I have secured from changes with a password, but that's not 100% fullproof.
I have come across other Web sites e.g. Goverment sites that allow you to download Adobe PDF Doc's that can't be changed. How do I go about transfering or turning my Word Doc into this sort of thing.
Or can a Word Doc be 100% read only without any chance of someone changing it?
Any thoughts? Thanks ;D
Without going into details (which I wouldn't anyway.....

I know I can send a 'read only' Word Doc that I have secured from changes with a password, but that's not 100% fullproof.
I have come across other Web sites e.g. Goverment sites that allow you to download Adobe PDF Doc's that can't be changed. How do I go about transfering or turning my Word Doc into this sort of thing.
Or can a Word Doc be 100% read only without any chance of someone changing it?
Any thoughts? Thanks ;D
