It depends on the type of file and what you want to do with it on the iPad. If you don't have an app that can read, edit or save the file, it doesn't matter what you do.
Email, DropBox, iOS file sharing with iTunes, third party apps for file transfer are all ways of transferring files from a computer to the iPad.
Read about using DropBox
About iOS file sharing
An example of a third party app
That would depend on the type of files.
For videos, music, photos, you use iTunes and sync them over.
For any other type of fiel, it will depend on the App used to open them as each has their own method.