Well, below are two ways to work with .pdf documents beyond just reading and/or printing them out.
1. Preview
For those of you who are using a Mac, Preview is Mac OS X's application for displaying .pdf documents. Preview gives users the ability to Annotate text. Once text is added, one just saves the document with a different name and then they can print or send to those people who need to read it with the new text.
Here's how:
Open the .pdf file in Preview.
Click the Annotations icon at the top of the window. When you do this, a set of annotation tools appears on the bottom of the window that looks like this:
You can then draw a text box by clicking and dragging from NorthWest to South East where you want the text to appear. You can manipulate the color of the text and the font as well using the icons available to you in the Annotate toolbar. (Unfortunately, text you type in a textbox is center-aligned and you will need to move your textbox to make your text appear where you want it).
You can use PDFescape for free to edit any .pdf document that you can read. Simply upload your file, or you can enter the url of an online .pdf file, and then you can add text, free hand writing, add images, or create drawings. When you have finished altering your document, you download the finished product to use as you wish. Have your students bookmark this site, and you'll be a little closer in your journey to go paperless.