Copy and paste are not allowed in the chatroom window by use of your mouse commands. If you want to copy and paste there, do the following.

To copy: Select the text you want to copy in the chat window. While holding down the CTRL key, press the C. This will copy the text.

Once you have copied the text, you can paste it using your mouse outside of the chat window in any other application, however you wish.

To paste: Cut or copy text from outside the chat window any way you wish. Insert the cursor in the message field and while holding down the CTRL key, press the V. This will paste the text.