This or an online remover?

There are a lot of web pages offering to strip invisible characters from your text. They work, mostly. The question worth asking is what happens to your text on the way.

If you clean a document once a month, a web page is a perfectly reasonable answer and you do not need to buy anything. This app is worth it when the problem is continuous rather than occasional, and when you would rather your text did not leave your machine to get fixed.