Unless you’re working on a scholarly manifesto, use normal vocabulary. Don’t try to be someone you’re not when you write; readers can tell. Be yourself. And by all means, don’t use words incorrectly. The book I first mentioned used strange word after strange word. I had to look up their meanings, discovering he had use the word wrong. Word does have a dictionary/thesaurus that’s so easy to get to. Use it, and use it often.
When writing you want to use as few words as possible to get your point across. Make sure you choose those words wisely.