Strip unnecessary formatting when pasting from Word to Wordpress textarea

I have a wordpress form, which is saved as a post when submitted. Users are not able to submit the form if the textarea has less than 160 words (there is also realtime word count). The problem is when user pastes his text from Word or any other editors, also the tags and other formatting is pasted. Then, even a short sentence can be more than 160 words. What I need is to add a realtime function, that will strip all the unnecessary tags and formatting, and will leave some the we want to keep (linebreak for example)