This addon is to be added menuitem to the Edit menu, the ability to convert simple text (plain) from formatted text(HTML text, rich text, etc) that has been copied to the clipboard.
You can paste formatted text (paste) in some web applications.
It means that you pasted formatted text(font size and color, alignment, etc) from Microsoft Word and Excel and other web pages.
However, instead of the formatted text, sometimes you may want to paste in the plane(simple) text (simple).
If the web page - can be copied as simple text (plain) using addon such as "Copy Plain Text".
But in Microsoft Word or Excel, paste it in Notepad then copy it again was required.
Now you can paste simple(plain) text without the Notepad to use this addon.