Unrecognized commands in simple PLT files?

[customwebprogrammer]

Hi, Fugazza!
I love the concept here - I'm using a plotter tied to a RAMPS 1.4 board, and HPGL is a great, universal plotter language. I certainly have some drawings that need optimizing.
Unfortunately, when I loaded a PLT file, I got an immediate error about unrecognized commands. I'm using simple PU, PD commands, so maybe I'm in a strange format, or need different line termination?
My files are coming from Inkscape, with "save as" HPGL
I'm attaching a screenshot, a 60kB HPGL file from Inkscape, and a simple "draw a square" file that all tripped up for me.
I look forward to helping with this project, perhaps with documentation?
I can be reached via email to henry(at)aciwebs.com
Simple 4 Squares plot file
Tuxedo Panda - 60KB file that needs optimization
Thank you!
Henry