This really depends what sort of file it is, but generally:Save a local copy of the file from the email, using the ‘save as’ command.Open the local copy in an editor. For PDF files most PDF readers have a limited ability to add text, such as using the ‘form fill’ commands. For other document types, you can normally just click on them and edit it. If it’s an image, I’d suggest Paint.net as it’s free and you can add txt to images.One done, save the document and close it.Reply to the email, click add attachment and attach the saved document, then hit send.