The standard in the industry is the Postscript Lanquage.
The majority of film houses will be Postscript compatible.
Keep in mind, most Service Bureau's cannot modify this file.
It is directly send to the imagesetter with only Resolution and Line screen being controlled at the film stage.

Everything from page size.(remember to allow 1/2in around for cropmark and bleeds) to the colors to output. Remember if you tell your computer to output 5 pages of 4color, and you only want 1.
You will be paying for 5. The responsibility is on you to ensure these files run fine...

To test the PRN files you can do a little test... From the Dos Prompt type the following
c:>copy filesname.prn lpt1

This will send the postscript file to your own Laser Printer, provided it is a postscript printer..

Setup...
If a Postscript printer is not resident on your computer. Try installing a Print driver for a Linotronic 330
Set the connection to file rather than an LPT port...That's it. Now when printing your file send it to this new printer. When you select print, It will prompt for a file name: Label it as filename.prn