According to the manual http://h10010.www1.hp.com/wwpc/pscmisc/vac/us/product_pdfs/3558793.pdf
these support direct PDF printing. You might try to connect with an FTP client and sending a PDF to them and see what happens.
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Alan Shore
Sent: Wednesday, December 31, 2014 9:54 AM
To: Midrange Systems Technical Discussion
Subject: RE: Printing pdf data from teh AS/400
I have been told the following
Alan, I believe they ARE HP4015 printers , and connect via tcp, Alan Shore E-mail : ASHORE@xxxxxxxx Phone [O] : (631) 200-5019 Phone [C] : (631) 880-8640 ‘If you're going through hell, keep going.’