If its the iPad specifically then a good starting point is to get an appointment with one of their Genius staff. That's their name, not my description of them. They will be able to give much more detailed explanations of what you can and can't do.
While its true that the iPad isn't intrinsically secure, can't handle a USB device plugged directly, to handle Microsoft files, the deeper truth is that amongst the thousands of apps available, there are ones that can boost the security of the file storage, can use MS file types, allow you to work on spreadsheets and word processing documents (in cloud service form or on the iPad), and there are plenty of physical adapters that will allow you to plug in a USB lead - although the device you're plugging in may or may not work.
I hardly use my laptop any more and a friend of mine uses her iPhone for all sorts of work, and she's in the healthcare profession. It's a very capable device but I personally think it is still just short of being a genuine and simple pc replacement. That applies to all the other tablets as well.
Security is really down to you, and that applies as much to your office computer as it does to anything else.
One more suggestion would be to find a couple of iPad forums on the Internet and ask questions there. People will be all too happy to give you pointers on how to do the things you need. The only downside is you will probably also find Apple-phobes equally happy (even if they're sad themselves) to tell you that it can't do these things and that you absolutely have to buy a Microsoft/Samsung/Nokia tablet.
I love mine, I hate the way Apple do some things, I hate MS software and use freeware, and love Windows. Horses for courses etc.
Good luck on your research.
