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.
A file with .svgz extension is a compressed version of Scalable Vector Graphics (.SVG) file. It is compressed with gzip compression and contains data in XML format. SVGZ files support transparency, gradients, animations, and filters. SVGZ files are smaller in size as compared to the default SVG files and this reduced file size helps transfer the graphics files.
You can also convert PLT into many other file formats. Please see the complete list below.