How can I paste unformatted text only
This can be done using a tiny (33KB) free (and portable) application called PureText.
You use a different keystroke instead of the normal ctrl+v to paste. Then it will convert the clipboard contents and paste "plain" text. I have mine bound to ctrl+q.
Have you ever copied some text from a web page or a document and then wanted to paste it as simple text into another application without getting all the formatting from the original source? PureText makes this simple by adding a new Windows hot-key (default is WINDOWS+V) that allows you to paste text to any application without formatting.
What PureText Will and Will Not Do
PureText only removes rich formatting from text. This includes the font face, font style (bold, italics, etc.), font color, paragraph styles (left/right/center aligned), margins, character spacing, bullets, subscript, superscript, tables, charts, pictures, embedded objects, etc. However, it does not modify the actual text. It will not remove or fix new-lines, carriage returns, tabs, or other white-space. It will not fix word-wrap or clean up your paragraphs. If you copy the source code of a web page to the clipboard, it is not going to remove all the HTML tags. If you copy text from an actual web page (not the source of the page), it will remove the formatting.
PureText is basically equivalent to opening Notepad, doing a PASTE, followed by a SELECT-ALL, and then a COPY. The benefit of PureText is performing all these actions with a single Hot-Key and having the result pasted into the current window automatically.
Source PureText
Disclaimer
I am not at all affiliated with PureText in any way but I've been using it for many years - it does exactly what it promises. PureText is completely free to use and portable.