Creating a download link in HTML is straightforward; add an anchor tag and point to the file within the href attribute. Some file types, however, (such as images, .pdf, .txt, and .doc for example) won’t be downloaded. They, instead, will be opened in the browser.
If you have server-side access to your website there are some workarounds you can use, such as configuring the .htaccess, to download these files directly. If your site is hosted with a free service like WordPress.com, Blogspot, or perhaps Github pages which don’t allow you to do so, consider using the download attribute.
Source files for the Tuts+ tutorial: Quick Tip: Using the HTML5 “Download” Attribute