We have all seen amazing sites using Flash throughout. As humans, we can appreciate these sites for what they are and often find them compelling and professional. But the simple fact is that a search engine spider cannot read the content of a Flash website.
Before you put a flash site up, look at the HTML code of the page you are presenting, and remember that is all the spider will see. Once you do that, nothing is left to be said on this subject, except that you may consider two versions of your site: One with flash, and one without.
We would also like to add that video runs great on Flash, and tutorial sections of websites do as well. But the main design will hurt your website more by using something that will help you be seen by search engines and load better for visitors.
https://www.mattcutts.com/blog/guest-post-vanessa-fox-on-organic-site-review-session/
If you must use Flash, you must also make an HTML version available. Block the Flash version from the crawlers with a robots.txt file. Vanessa Fox. 2006.