The
Baen free library offers a lot of free sci-fi books for download. One of the highly recommended ones (though I've yet to read it) is
On Basilisk Station, the first in the Honor Harrington series. (The
second book is also free.)
They don't offer these books in PDF, but you could use the HTML version and put the unzipped folders on a disc. He'll be able to open them in any internet browser.
Alternately, if he has the ability to install software on the computer (is it his computer, or a public computer?), you could send him the installation file for a common ebook filetype. I would suggest the ePub format, though I'm not familiar with all the software. I use Calibre, but I primarily use it as an ebook library management tool... it's overly bloated if all you need is a reader.
The Suvudu Library sometimes offers PDF shorts from SF&F magazine. Here are a few I found:
http://sf-fantasy.suvudu.com/2010/11...-magazine.html
http://sf-fantasy.suvudu.com/2011/01...is-lawson.html
http://sf-fantasy.suvudu.com/2010/09...y-ken-liu.html
http://suvudu.com/2010/08/suvudu-lib...-mcmullen.html
http://sf-fantasy.suvudu.com/2010/07...-addition.html