The robots.txt file will prevent Google from crawling a specific page or set of pages. However, Google will still be aware that the URL exists – especially if you link to that URL internally, include the URL within your sitemap.xml or that URL is linked to from an external website. In this scenario, a robots.txt will not prevent Google from indexing the URL itself. This could lead to the URL being returned in the Search Engine Results Pages (SERPs) with a warning that robotst.txt prevented them from crawling the page.