PDF Expert is one of this apps that I use all the time. This is the app that I run all my non music documents through. I use it to keep track of anything sent to me via email especially. This is the app I use to fill out entry forms, contracts, to sign membership papers and all sorts of things teacher related.
It is free currently and it normally costs $10! This week only though I believe!!!!! So hurry! You would be crazy not to grab it at normal price but while it is free it's a no brainier!
The capabilities are extensive so watch a few of their videos and read their website to get an idea of the possibilities!