Following the invoice and quotation, Linda and Axel continue with the PDF Invoice object.
Here's what they discover:
Buttons
Draft
First, they create a draft PDF Invoice.
Only the Edit and Delete buttons are displayed:

Proforma
Next, Axel suggests creating a Proforma.
Now the Send proforma by email button is also displayed:

Invoice issued / Duplicate
Linda then compares it with an issued invoice.
After issue, the Send proforma by email button is replaced by Send invoice by email.
Out of curiosity, they then create the Duplicate on this invoice.
The button remains the same in this case.
Tab: Essential information
The fields in this object are not conditioned.
Given the number of fields, there is only one tab in the page layout:
