Three possibilities --

1. Scan the books and use Microsoft imaging's OCR method to turn it back
into text. Bit tedious if there a many pages, but it will work reasonably
well.

2. Open the prn files in Word using the 'Retrieve text from any file' option
under 'Files of type' on the File > Open dialog. You'll certainly retrieve
the text that way, but possibly with so much extraneous guff that it's
unusable.

3. If the prn files are plain PostScript (which they should be, if output
was destined for an Apple LW) and you have or can borrow a copy of the full
version of Acrobat (not the reader) -- change the file extension from .prn
to .ps and see what Acrobat Distiller can do with it. With luck, it will
display the file correctly; and from Acrobat you can save as Word.

Print the files on the Laser Writer, then scan the printed pages into
an OCR program to turn them back into text.

There is no way to read the text directly out of the .prn files, which
are just the printer's instructions for formatting the pages.

--
Regards,
Jay Freedman
Microsoft Word MVP         FAQ: http://word.mvps.org