Use the drop-down field to provide your users with multiple options; for example, selecting their home country. In the web form, this appears as a classic drop-down menu, like in the example below. However, in a PDF it is rendered as a text list.
In many cases, the Value and Label could be the same. But, you have the freedom to use different labels if you wish. For example, you might want to use country names on the Web Form and country codes on the PDF.