You can Control "S" every page of the topic. This will save an HTML copy of the page. To have a copy of the whole topic, you would need to save every page.
You have the option of saving all the information on the page as well, but I rarely do that because it takes way more hard drive storage to do so. If you saved all the information, just remember you need to be careful using the information as it may have copy writes prohibiting it from be published again.
Once you do this, then click on the file in Windows Explorer or however you view your files and it will bring up a locally stored copy of the webpage. This works in Firefox and Chrome in Windows. It may work in other browsers and for Apple, but I don't know what the actual keystroke would be for any of the other systems. Only other thing to remember, when you click on a link or to change a page, it will go to the actual page and the website's server, not your stored copy. To see the copy, you would need to click on the file for the other page itself, not the link to it in the stored copy of the webpage.