An apparatus comprises an operating unit (31; 58; 131), which can be a welding unit (31; 131) for welding a closing film (22) to an edge zone (41) of a containing element (3) or a separating unit (58) for separating containing elements (42) from portions of sheet material (62), said apparatus (21; 61; 81; 161) comprising a control unit (CU2; CU3) programmed to enable said operating unit (31; 58; 131) to process selectively a continuous strip of containing elements (3; 42) or discrete groups (118) of containing elements (3; 42).