Does the attachment include the name of the document? Usually the very end will have the extension.
The name should be something like Laundry list.doc.
What happens if you press and hold a finger on the attachment? Do you get a list of options for what you can use to open the attachment? If so, and one of them is Mail, try picking it to see if that helps.
If your'e not seeing the name of the file and the extension, it may be worth removing The Vault from one device, just to see if you can open the attachments as usual. If so, that suggests a problem with how the app was designed to work with iOS.
~Lyssa