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.
Files with .DOC extension represent documents generated by Microsoft Word or other word processing documents in binary file format. The extension was initially used for plain text documentation on several different operating systems. It can contain several different type of data such as images, formatted as well as plain text, graphs, charts, embedded objects, links, pages, page formatting, print settings and a lot others.
You can also convert PLT into many other file formats. Please see the complete list below.