To reply to an email and attach a file, go to Gmail on your computer and click Reply. Then click the Pop out icon at the top right of the email. In Gmail, click the paper clip icon at the bottom of the email and select the edited file from Google Drive. After providing a reason for the edited version, ask the recipient if they would like to receive it. Another option is to select multiple emails and click "Forward as attachment" from the overflow menu. To send an email as an attachment, click the paper clip icon while composing the email and select the file. This allows you to provide a summary message and attach supporting emails.