TLDR: Get an ImageWriter II with a sheet feeder, or use a virtual PDF printer on the Plus and transfer the PDFs with a null modem cable or network adapter and then print them from Acrobat Reader. I highly recommend getting a SCSI ethernet adapter because it will greatly ease file transfers and you can browse the web (to an extent) on your Plus. If you have the choice of spending money on an ImageWriter or Ethernet adapter, go for the adapter.
Three questions:
1. Is it fully loaded with 4 MB of RAM?
2. Are you running System 7.0.1 or 6.0.8?
3. Do you currently have a method of transferring files to and from your Plus?
An old ImageWriter would probably be your best bet since it's Dang near impossible to find ink cartridges for the StyleWriters, and shipping on a 50-pound LaserWriter II will be horrendous. You should still be able to find ink ribbons for them, and I believe the ImageWriter II has an optional sheet feeder so you can't have to track down cases of accordion-fold paper. (You could probably even rebuild an old ImageWriter ribbon using the modern ribbon from a cartridge designed for something else.) Some later networked HP laser printers like the LaserJet 4000 have LocalTalk capabilities. Look around and see if you can find one of those cheap; they have Ethernet as well and lasers are cheaper per page than inkjets for printing black and white stuff.
If you have a PostScript-compatible printer at home, you can use the stock LaserWriter driver to make raw PostScript dumps you can send to your printer from your PC. In the Print dialog box on the Plus, click the "file" radio button. Then transfer this file to your desktop PC and print it using a utility that can send raw PostScript such as
PrintFile. Additionally, some Adobe products such as Photoshop and Illustrator should know how to import PostScript files and render them to a Letter size canvas.
If you're running System 7.0.1 (or later) on it, you can try the free
PrintToPDF tool. You install it like any other printer driver on your Plus (Drop it on your System Folder), and it spits out PDF files. You can then transfer them to your PC and print them with Acrobat Reader, just like any other PDF. I'm not sure how well this will run if you're tight on RAM, and it requires System 7, but it's a Heck of a lot easier than the last file solution.
Mac printer cables can act as null modem cables. If you can find one with a Mini-DIN on one end and a DB9 on the other, all you need is an adapter to switch the gender of the DB9. Alternately you can use two modems. This might be easiest since you probably already have a 56k modem for your PC around somewhere, be it in a box in the attic or a PCI card. There are more details here:
http://www.macwindows.com/peertips.html#crossover
The most straightforward way to move files in bulk that I can think of transferring is a Zip drive. A SCSI drive connected to your Plus with a USB drive connected to your PC should work. As long as the Plus is running System 7 it should be able to understand FAT. You can then print the files off the Zip disk.
(Now excuse me while I go off on a tangent about different options and scenarios that will work as well.

)
I'm not sure if this will work or not, but you could try setting up a virtual Mac on your desktop PC using the Basilisk II emulator. It takes a bit to set up, but it just might be able to read 800k double-sided floppy disks. (It will certainly understand the file system.) Then you could use the "My Computer" icon on the virtual Mac's desktop to drag the PDFs or PostScript files off the floppy and into your PC's file system.
Another option would be using another old Mac with Ethernet that can talk to the Plus via AppleShare. (Or you could shut the Plus down, unplug the SCSI drive, and hook it up to the newer machine.) Then it can upload the files to your PC through FTP.
Probably the hardest method with the most reward would be to get a hold of a SCSI-to-Ethernet device, or a LocalTalk-to-Ethernet. This would give your Plus access to the network (even the entire Internet), and you could use an FTP utility like Fetch to upload the PDFs to your PC or a VM running an FTP server. Another slightly less old Mac can work as a bridge. I know for a fact a LocalTalk bridge will get your Plus online; that's how I did
this with my SE.
Unfortunately the Plus does not support the 1.4 MB SuperDrive floppy drive, so it cannot read DOS floppies. If your PC has a floppy drive and you have a newer Mac with a SuperDrive, you can go from the Plus to that using LocalTalk, then to from the newer Mac to your PC via floppy.
Also that's not exactly a "parallel port" your hard drive's plugged into, that's SCSI. It's your high speed (relatively speaking) data connection to external devices like hard drives, storage devices, network adapters, and scanners. As long as you assign each device on the chain its own unique ID (you can daisy-chain 7 devices) and have a terminator on each end of the chain, the SCSI voodoo won't bite you. Both of the Plus's serial ports (Modem and Printer) are Mini-DIN. The smaller D-sub port is for an external 400k or 800k floppy drive. It's important to note that
only the serial ports are hot-swappable! Do not unplug or plug any plugs while the Plus is running! Do not touch the SCSI chain until every device plugged into it is turned off!