I am pretty certain it is not possible to add own drawings, but either way Documents to Go is awesome. Maybe Evernote is something you'll want to look into? I use Evernote all the time.
So what is Evernote anyway? Imagine you could create notes, record audio clips, take snapshots or even upload files and have all of them accessible at anytime anywhere with synchronization between your computer and mobile phone. Sounds great, no? Evernote supports iPhone, BlackBerry, Windows Mobile, Palm Pre and soon Android. Sounds good now? Definitely! With dedicated software for Windows and Mac OS X as well as a simple yet intuitive Web interface, you can have all your data out there in a cloud with Evernote and access that cloud from school, home or work. Did I say it's free too? With 40MB monthly quota you can have your productivity set at the maximum and still have your life organized.
Say you are in class, open Evernote on your iPhone and start taking notes with it while you're listening to the professor. After class you have the opportunity to use a computer with Internet access. Head over to the Evernote Web client and edit your notes you took with the iPhone; maybe you want to write some details of the quick notes you took while in class. No software required, you can access the Web client on shared computers too. Once you save your note, it will be automatically synchronized over the air and you can see the changes instantly on your iPhone. There are many possibilities. If you're a power user and 40MB isn't enough, for as low as 5 USD monthly you'll get much more monthly quota (500MB) and additional features such as upload of files of any type and format.
Sounds great, no? Combine Evernote with Documents to Go, you'll have a very solid and powerful combination that's definitely helpful for success with your studies!
http://www.evernote.com/