unlocking 'locked' PDF files
I have a PDF sent to me that is locked. I want to be able to make notes on it on my iPad and send it back. Currently I am printing off the PDF document, making the notes with a pen, scanning them and sending the scanned copy back via e-mail. I've seen a number of iPad apps that allow me to make annotations on PDF files, but unfortuntely the PDF files I get sent to me are locked. Is there any way I can 'unlock' it and make annotations on it using some of these apps. (I am looking at getting iAnnotate for iPad). Any suggestions?
iMac, Mac OS X (10.6.5)