how do i open an .rdf file from email and display in an ipad?

You need an app capable of viewing it. It is possible there are some alternate iOS browsers that do, but I have my doubts. You might do a search on the app store.

I don't think you will find on. I just looked, and the hit on the search was for a feed reader, that I think is not in the same context as your question.

My only suggestion would be to ask the send to send it in a different format, or from another computer, rename the file. I suspect that if you gave it a .txt extension you would be able to open it and read the elements.