For example, an uploaded .rtf file is still a .rtf file. You can't perform FirstClass actions, such as searching, on an uploaded file.
import the file
The file is converted to a FirstClass document if possible.
This means that you can perform the same FirstClass actions on these documents as you can on any other FirstClass document. If FirstClass can't convert a file, it will be uploaded instead.
You can upload and import a folder just as you would a file. In both cases, a folder is created in FirstClass. The folder contents retain their file types.