Hi wals4
Greetings! I am Andrew M, an Independent Advisor. I am here to work with you on this problem.
Send Email command can be found by clicking on File > Share > E-mail, by then Windows attach your current file to an e-mail using Microsoft Outlook as long as you have it configured as your default e-mail software manager. Now, as you claim that you can't close Microsoft Word until you perform that action, I can recommend you to switch a new message first (new Outlook e-mail) and either you can send or close the message.
If you try to quit or exit Microsoft Word before sending your email with the Word document attachment, you will receive this error. To send your email, ensure Microsoft Word is still open in the background.
Any further doubts you might have, please let me know.
Best regards,