LdiJ, while it may seem impossible that something as common as legal forms and documents are copyrighted, they are, in fact, copyrightable.
The legal language often remains the same from form to form and document to document, as in most cases it must, but variations in how the agreements are worded allow for copyright protection. Copyright protects the
expression of the facts and ideas (but not the facts and ideas themselves).
Because there has been the rare lawsuit filed in the past over the unauthorized uses of a company's legal forms, it is wise to have your own drafted. The odds of being discovered and then sued over the use of someone else's forms may be slim, but there is still a small chance you can be.
And anyway, doing something illegal just because you can probably get away with it is never the wisest way to operate, nor is it advised.
There ARE free forms available that you can fill in yourself, and you can use the facts and ideas provided in another's form to create your own, but you have to be very careful when you take the words of another and use them for yourself. Fair use of another's copyrighted material is only determined by a court AFTER you have been sued for infringement, so the Copyright Office advises that a person get permission from the copyright holder before using any copyrighted material. One cannot rely on fair use to protect oneself from an infringement suit, nor will a fair use defense always be enough to defeat an infringement claim.
For the best legal protection, you will want any legal document tailored specifically to your own needs, and you will want to ensure it protects both parties from any misunderstandings over the language used. This means a person should have an attorney draft any important legal document to ensure it says all that it needs to say to protect both parties from any dispute in the future.