Visa Extension means that you will have a new permission to further stay in Vietnam without leaving and reentering the country. By this action, you will get an extension stamp on your passport indicating your new stay duration.
Vietnam Tourist visa DL (categorized as DL) is one of the most popular types of Vietnamese visa which is valid for up to 3 months (Single/Multiple entry) and can be renewed for one time after arrival in Vietnam.
If you're planning to do a business visit in Vietnam, you need to get a business visa. A business visa (Categorized under DN) is a short-stay visa, which allows its holder to enter and remain in Vietnam for a maximum period of 12 months