We often see the first or all letters being capitalized in western legal documents and agreement forms, or in the case of characterizing or emphasizing the subject in a statement in journalism.
The example, "WITNESS WHEREOF, the parties hereto have caused this Agreement to be signed" you suggested looks very odd, if it's done in an official Japanese language document.
We don't do that in legal or official documents written in Japanese because we don't have capital letters. If you want to emphasize a particular word or phrase you can show it with a bracket - . But it's uncommon to do so in Japanese language legal forms, and you don't need to venture to do it.