Can not edit Pages files in Dropbox in my iPad

You have to send them to the Pages app on the iPad using the arrow icon in the upper right corner of DropBox.

Launch DropBox, tap on the Pages file on the left side. The file will open. Tap the arrow icon in the upper right corner and select Open in Pages.

But then once you've made changes to your document in Pages, how do you get it back into Dropbox so that the changes you made on the iPad are updated on that same document when you access it through your other devices?

There is no direct way to send files from Pages to Dropbox. Though what you can do is email the document to yourself, open your mail app and locate said email to yourself, tap to download the attachment, then tap and hold, select "open in..." and choose Dropbox. (note: for this to work the Dropbox app must be installed on your iPad)

Or get a @sendtodropbox.com address; http://www.sendtodropbox.com/

Interesting. I had not heard of that service. How safe is it though?

Yes

you can edit any Docs in your Dropbox on you iPad by Cloudon