A handy little app I use once in a while is called Zosh. You can download it from the iPhone app store. I'll preface this by saying it is still a little buggy, and not ready for iPad, but for the most part it works great. Very simple process. You send a pdf copy to Zosh - click on it - sign - adjust - and email it to whomever you want. I use it mostly for when I have to sign for strata documents. I have all the strata companies pdf sheet already on Zosh so when I need documents I simply select the documents I need, sign and email. No need to print. I've also used it, as I explain in the video, after negotiating a deal that has gone back and forth a few times I needed one initial on one page. The Buyers REALTOR® emailed me their signed version, I sent it to Zosh, met my clients at Earls and had them initial on my phone. Everyone got an emailed copy and I didn't have to waste 1/2 hour running to my office to print off the one piece of paper.
Again, not the best system for doing a full contract on, obviously the size of the phone makes it hard to go through a large document, but for quick initials or signatures it's definitely come in handy.