PDF is not an ideal form for reading ebooks. I would get the ePub version from Smashwords and then use a desktop ePub reader on your computer, such as the Nook application or Adobe Digital Editions. ePub makes a convenient format for reflowing text, adjusting the size for comfortable reading, etc. PDF is a static format.
I personally read ebooks on my iPad or my iPhone using Stanza. But the desktop version of Stanza is, I think, not that great (though I haven't tried it recently). You could try Stanza on your computer too though. There are a bunch of different programs to read ePub books on the computer; try a few and pick the one you like best.