You can always open pages, then open a second app, then double-click the home button quickly. That will pull up a list of recently opened apps. If you hold down on the Pages icon, it will eventually bring up an X. You can close out of it that way. Then click on the icon on your desktop to restart it.
I have never had a problem with Pages freezing, so there is the possibility that you might lose some recent work if it locked up & hadn't saved it yet, but if you're willing to risk it, that should unlock the app. I've used the same method to unlock my calendar app many times & it has always worked fine.
What iPad are you using, btw? I had a lot more issues with apps freezing on my original iPad than I have had on my iPad 2. I think that the extra Ram really helps.