welcome, @Jacob. I do not know the answer regarding the export of HPGL format, perhaps @slspencer could help with this.
Sadly, the import of a DXF file will not be implemented any time soon because the DXF is a vector graphic representation and the information used to generate the pattern is not included. This was first answered here: Will be Importing DXF available?
You may also see an earlier discussion about the HPGL format here: Difference between PLT and HPGL
and, in general, if you wish to see if a topic has previously been discussed, you may use the search icon at the top of the window on this forum