From the screenshot, you don't actually have "pure text" but instead are pasting in content from a webpage.
When you cut and paste from a website into most word processors, you carry over the HTML formatting with links and all that.
If you paste directly, you'll see all the links appear in the document.
To cut and paste without all those links or formatting go do the following when you're in the document (after having already selected and copied the text to the clipboard):
Edit > Paste Special... > Unformatted text
This will drop in just the text you've selected.