how to add .html extn end of all page/post url in wordpress

[admin]

We developed a html static site to WordPress (CMS) blog site ...

For SEO, Static url for best SE cache/crawl...<br>
<strong>Best way to On crawling and indexing sites for the Google index..</strong>

Dynamic URLs vs. static URLs details ref <a href="http://www.doordie.co.in/seo/160216" rel="nofollow">doordie.co.in/seo/160216</a>

So, how add

.html

extension end of <strong>all page/post url</strong> in wordpress <strong>without plugins</strong>

For eg.

chennaitechnologies.com/google-adwords/

To:

chennaitechnologies.com/google-adwords.html

Any code or

.htaccess

possible?