[Faterson]

To delete a file from Dropbox, swipe your finger from right to left across the file-name. A red "Delete" button will appear. That's the standard method of deleting things in iOS.

As to the various file types, Dropbox should always automatically suggest an app for you to open a file in. It suggests music or multimedia apps for my MP3s, video apps for my movies, etc. etc. Just tap that arrow icon in the top right corner of your screen after downloading a file from Dropbox. A list of apps will appear in which you can open that particular file type.