An HPGL(Hewlett-Packard Graphics Language) file contains an instruction set for plotter control, developed by Hewlett-Packard. Hewlett-Packard plotters use this file to draw and print vector and raster content on the paper.
Enhanced metafile format (EMF) stores graphical images device-independently. Metafiles of EMF comprises of variable-length records in chronological order that can render the stored image after parsing on any output device. These variable-length records can be definitions of enclosed objects, commands for drawing, and graphics properties critical to render the image accurately.
You can also convert PLT into many other file formats. Please see the complete list below.