You can customize the Invoice, by changing the Invoice PDF title & labels, adding custom fields for document, item and company details and by changing the settings of the document.
Please check the below link to know to do the customization.
For Invoice PDF title and label customization, please check the below link.
For adding Custom fields please check the below link
Company custom field : How to add custom field for company on web?
Document custom field : How to add custom field for the document on web?
Item custom field : How to add custom fields for the item on web?
For the changes to make in document settings, please go to Document settings >> Enable the required toggle as per your business needs, like showing images, showing payment, hiding quantity etc.
