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.
The XLTM file extension represents files that are generated by Microsoft Excel as Macro-enabled template files. XLTM files are similar to XLTX in structure other than that the later doesn't support creating template files with macros. Such template files are used to generate and set the layout, formatting, and other settings along with the macros to facilitate creating similar XLSX files then.
You can also convert PLT into many other file formats. Please see the complete list below.