How to create an activity that reads document files?

Question

This is my problem. I am creating an android app that is suppose to download documents i have stored on my server to my smart phone and opens the document WITHIN my app. So essentially I want an activity that will be able to open the document after it has been downloaded to the phone and display it in the same format it was in when it was originally uploaded. In a sense, it will act like one of those documenting reading apps that are on the play store. Thanks for any assistance. However, users will not be able to edit the document, they will only be able to read it.