Can the File Attachment functionality encode a file to base64?

I have attached a file to a REST request to upload to an application and it uploads it ok however when I open the file in the application it says the file has been corrupted and I can't view it. The file needs to be base64 encoded which is why I think it is giving this message. Is it possible to make sure the file is encoded as base64 when attaching it to a request?