@Don1carter,
Welcome to HP Forums, this is a great place to get support, find answers and tips.
Thank you for posting your query, I'll be more than glad to help you.
I understand that you wanted to know if you can print more than one envelope with only one print command from your HP ENVY 7640 e-All-in-One Printer.
This issue could occur if you are not using the mail merge option in Word to print the envelopes.
Let's go through a few steps to resolve this issue.
And here's the step by step guide for you in the link: Mail merge with envelopes
You may also check the link: Printing Envelopes (Windows)
Also, let us know if you have installed the latest drivers for the unit.
Let me know how this works.
You have a good day ahead.
Rainbow23 - HP Support.