Hello kozak-steven,
You'll want to upload a Microsoft Office 2010+ (*.docx) file and make sure that the document is less than 2MB.
Please visit Microsoft's website for the steps to upload.
Once done, go back to Custom form styles and import your invoice again.
Feel free to read this article for more information: Import custom form styles for invoices or estimates.
You might also want to visit our page for future reference: Manage customers and income.
Please let me know if you're referring to something else. I'll be around to help you further.
