If it is genuinely unique information that cannot be found elsewhere and is entirely your intellectual property, then make recipients sign a properly drafted NDA before release.
Yes, NDAs are not watertight ..... but at least it gives you a more solid legal foundation than you might otherwise have. It also tends to make people think twice before disseminating your document.
But in the end, the only real solution is the old "air gap" firewall. Document is on a computer, not connected to any network, cables superglued into their ports and unused ports superglued off. People have to sit at that computer to read the document. (assuming you don't start wearing your tin foil hat and worrying about people reading the document through EMF, or your house being bugged, or your phones being tapped, or..........
).