I want to take a posting to talk about annotating PDF, Word and PPT files with a great FREE site called crocodoc.
This site works really well with your Chromebook. You DO NOT need an account to use it, but if you set one up, it gives you extras like file listings and larger file uploads.
The trick here is uploading a file to them by browsing to your "downloads" area on your Chromebook or selecting the file from your Google Drive (I prefer this option).
Once uploaded you can Draw, Comment (sticky note), Add text, highlight, and strike thru with the tools they provide.
Account (or not) you can Share the marked up file by using the SHARE button...
It will send a link to others, email the marked up file, or give you the code to embed into your blog or website.
You can also share files and folders from the Directory...
You can also DOWNLOAD the original file or the marked up file...
This a great tool, easy to use and works with Mac OS, Win OS and ChromeOS (Chromebooks and ChromeBoxes).
Now, the WHY...
Sometimes you want students to be able to annotate (markup) a file...maybe its a PDF worksheet, a WORD document or an image (say a Map or Diagram).
They can upload the document from you (Share it into their Google Drive, or send them a DROPBOX link that they can download, then upload).
Once in their Crocodoc, they can mark it per your direction... for example, identify features of the map, find and correct grammatical/syntax errors, fill in the blank with the TEXT tool, etc.
Easy and Free -- great things to be!
Give it a try at http://personal.crocodoc.com