I would like to ask if it is possible to do the following:
Avoid duplicating the same page in the browser tab. I explain, I have a link that is www.registrar.aspx, I want that when you copy the link and paste in another tab do not load and there is no duplicity of pages.
Sorry in advance not to put the code
From what I understood you could have a problem with the Cross-site Reference Forgery (CSRF) vulnerability, which means that from another page (tab) the user can be spoofed to send information to the server through a post request.
If that was the case it's from Anti-Forgery Tokens. ASP.NET has Anti-Forgery Tokens to prevent counterfeiting of requests between sites. Implementing does not matter if they duplicate the tab because it will not allow the sending of data, it is also capable of stopping an attack from another site. There is a lot of information on YouTube and Google.
Now if the matter is a simpler one I suggest that you handle it with JavaScript. Disabling the right click and copy and paste on that page. There are also sample numbers on the internet about how to do that.