PACs emulate a PLC, do motion control, Ethernet networking with other computers, data transfer, etc.
Note: PAC are designed to replace PLCs, but also to replace DCS systems too.
That fact, plus the fact that industry is moving towards IIoT and Industry 4.0 (PLC to SQL to OPC, to PC network security, to HTML5 like in a SCADA system), computer programming is a necessity for the industrial engineers graduating today. If you are in school and the instructor refers you to a printed book, keep in mind, most are outdated by the time they are printed. If the school is up to current times, most of your references should internet or digital books that can be updated each year.