It's difficult to define something so general. You would have to specify more what you really need, or the file type. Then you can have a look at the .NET Framework itself, there are a lot of "XXXReader" classes, for example:

• BinaryReader
• TextReader
• StreamReader
• StringReader
• XmlReader
• XmlTextReader
• IDataReader
• EventLogReader
• XamlReader
• EntityDataReader

And each one is really different from the others... Some are abstract, some aren't, etc...