Redirection impact in SEO ?

For example my page url - xyz.com/abc now we are converting site in html page now the url - xyz.com/abc.html
old url - xyz.com/abc
new url - xyz.com/abc.html

Is this condition affect my website seo or not if yes that how to mapp old to new because we have more than 150 pages how to redirect all url

just 301 redirect old URL to new URL and re-submit / re-ping the sitemap... 150 pages is not much, you can do it manually