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 .TXT extension represents a text document that contains plain text in the form of lines. Paragraphs in a text document are recognized by carriage returns and are used for better arrangement of file contents. A standard text document can be opened in any text editor or word processing application on different operating systems. All the text contained in such a file is in human-readable format and represented by sequence of characters.
You can also convert PLT into many other file formats. Please see the complete list below.