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 OTT extension represent template documents generated by applications in compliance with the OASIS' OpenDocument standard format. These are created with word processor applications such as free OpenOffice Writer and can hold settings that can be used to generate new documents from these template files. These settings include page margins, borders, headers, footers, and other page settings. Such templates are used in official documents such as company letterheads and standardized forms.
You can also convert PLT into many other file formats. Please see the complete list below.