Display the Estimate number on an Invoice that was generated from a Sales Order.

When an invoice is generated from a sales order which was created from an estimate, the Created From field on the invoice shows only the sales order number.  To show the estimate number:

1. Navigate to Setup > Customization > Transaction Body Fields > New.

2. Provide a Label.

3. Type field select Free-Form Text.

4. Unmark the Store Value checkbox.

5. Under the Applies To tab mark Sale.

6. Under the Display tab > Subtab select Main. 

7. Under the  Sourcing & Filtering tab

• Source List > select Created From.
• Source From > select Created From.

8. Click Save & Apply to Forms > select your preferred invoice form.

9. Click Save.

Note: There is a related enhancement for this under Issue 99329.