The latest Official Release of HDF is 4.2.13
HDF4 (also known as HDF) is a library and multi-object file format for storing and managing data between machines. There are two versions of HDF technologies that are completely different: HDF4 and HDF5. HDF4 is the first HDF format.
Although The HDF Group maintains HDF4 by fixing defects and porting it to new operating environments, there is no longer any new development occurring. HDF4 is considered deprecated and new products should be developed in HDF5 . See this FAQ for details.
Specification and Developer's Guide