Receipts for MemberMouse are in email format with a PDF attachment. If you're not receiving the receipt in this format, please submit a ticket so we can look into it further.
BONUS: We do this using the MemberMouse PDF Receipts Plugin and you can too!
We consider that your monthly email receipt from MemberMouse serves as an invoice. If you have particular requirements about what information needs to be included on the pdf, you can follow the instructions outlined here: Customize Billing Information on MemberMouse Receipts