You are being paid for original information and thus should never copy and paste text from other websites into a blog post. However some people prefer to write their posts in a word processor and then copy material from that program into WordPress. On rare occasions, you might want to post information from another site and then edit it to be in your own words. In either case you need to be aware that when you copy and paste that text, you are also copying and pasting formatting of that text. This can cause your article to look odd or unprofessional.
To kill all the formatting when you import text do the following. Before you past the text into the article, click on the HTML tab. It’s found on the right side of the formatting bar. The formatting bar is that bar of buttons just above where you enter your text in your article. Click HTML and then paste your text. Then click Visual and continue to edit and write as you would normally write.