If you have to ask, you probably already know the answer. A more important question is what do you plan to do with the files, and is this use allowed by the terms? If it is, then you can possibly ask the site to allow you access to download them. It is possible that they disallow crawling just to reduce load on their servers, and so crawlers don't waste time on text files when there is more valuable content to crawl elsewhere on the site.
