I have been searching for this answer and this is super useful functionality that will improve everyone's life who uses Ubuntu 18.04 LTS. Basically, in a terminal in putty you can highlight words with left click and with right click you can paste
So basically go to Settings -> Universal Access -> Pointing and Clicking needs to be set to medium speed. I had mine set to lowest setting. Now you can double click a word in the terminal and then with middle click you can paste. You don't have to drag and highlight a word and then right click, and then select "copy"