According to WebAIM, making hypertext links accessible is one of the most basic and most important aspects of web accessibility.
WCAG 2.0 Guideline 2.4.4 (level A) - The purpose of each link can be determined from the link text alone or from the link text together with its programmatically determined link context, except where the purpose of the link would be ambiguous to the users in general.
It is a best practice to let your website users know when they select a link that it may lead them to non-HTML resources such as PDF files, Word or Excel documents. To do this you should add the document type within the link. Here is a list of the primary document types used on the UNG website: