File Types and Extensions
•The decision to transfer a file using binary or ASCII mode is largely determined by noting the file’s  type.  The file type can be determined by its extension.
•
•A file extension is the last three characters following the period in the filename. 
•
•You can download files with a file extension of .txt or .htm or .html in ASCII mode.
•
•You should download files with other file extensions (.doc, .xls, etc.) in binary mode.