This output in Menu File / Input/Output Formats / File transfer/Documentation / "HPGL generic output" generates a *.plt file of your TARGET 3001! project in HPGL format

Hpgl e.png

Basically it`s useful for to transfer coordinates of your project into other systems. For example if you want to know whether your PCB Outline is fitting into a special housing which you have drawn with another CAD System, you may import your TARGET 3001! project in HPGL format. Another option was the *.IDF format or the STEP format in this respect.