The WinMTR can be copied and pasted directly in your reply… it’s usually a small amount of text.
As for the more general question of why you cannot include a link… It has to do with your “trust level” (I hate this name, but that’s what they decided to call it). The trust level is an indication of your activity on the forums. Everyone starts at trust level 0… with time and forum participation, your trust level increases. See this post for more details:
Until you reach Trust Level 3:
To post a link, write it (or copy-paste it) as you would normally in your post, highlight the entire link and click on the </> button in the formatting bar at the top of the input window. That will transform your link into “Preformatted text” and will be allowed by the forum software. Your link will appear as : https://www.google.com