Much like any other image, even HP plotter graphics (*.hpg) files can be exported as common PDF documents. Useful for sharing, but the file won't be useable for plotter purposes anymore.
Convert HP Graphics Language plotter document to Adobe Portable document format.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert hpg to pdf on Windows
Leading 2D and 3D CAD development software from Autodesk
Convert from hpg file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.