Writers often read other writer's works in draft form. We critique, proofread, review, and blurb.
In the old days, the other writer would send you a printout by postal mail. You'd carry around a sheaf of paper, scribbling furiously in the margins. When finished, you'd package the marked-up copy and take it to the post office for mailing back to the author.
Things got even easier when it became possible to email versions one could review. Microsoft Word, for example, has a review feature that tracks comments. Starting with version 10 of the free reader, Adobe Acrobat allows you to highlight and make simple comments.
When I got my Kindle, though, I wanted to be able to read copies there. My Kindle is much more transportable than a laptop or even my netbook, and the screen is much easier to read than that of a smartphone.
Kindles can read PDF, but it doesn't read well; typically the font is too small and when you resize it, the text doesn't reflow. I wanted something that would behave like a regular Kindle book, with all the features.
Kindles can read something called the Mobipocket format. (See the WikiPedia entry "Comparison of e-book formats.") Without too much pain, you can download a free copy of the Mobipocket Creator, create a .mobi version of your Word, PDF, text, or HTML document, and then put it on your Kindle.
How? If you're adventurous, go to the Mobipocket software page, download the Creator (on the right side of the page), and give it a go. (Import, optionally enter metadata, and then build.) If you need a little more assistance, check back later and I'll post the full instructions.