Address your message as normal. Go to the main part of the message and write in details of the file you are sending. This will help your correspondent sort the file out on receipt. Now you can send your message as normal. If your correspondent cannot cope with attachments or coded files, you may have to send the file as ordinary message text.
Text files are files made up of the ordinary letters, numbers and punctuation found on the keyboard.
They are not word processor files. See Transferring Files Between Computers for how to transfer files. Word processed files saved as text lose all their formatting and styles and any graphics will disappear. You are asked for the name of the file which is then inserted into your message. You can also list and select from other directories.