DPF or Diesel Particulate Filter is a honeycomb configured, ceramic filter installed inline in the exhaust stream and are used to reduce/eliminate the visible particulate matter (PM) or soot, from the exhaust of diesel engines.
A DOC (Diesel Oxidation Catalyst) is similar in size/shape/location to the DPF and it reduces the N20 (Nitrous Oxide) in the exhaust, as well as an EGR (Exhaust Gas Recirculation) loop which pulls raw, untreated, exhaust directly from the exhaust manifold and plumbs it back into the intake of the engine.