• Go to 'Settings' tab.
• Click on the 'Organization' sub-link.
• On the Organization Settings page, click on Custom Fields.\
• If you want to create the custom field for estimate, then click on 'Estimate' found on the left side of the screen like in the image shown below. Ensure 'Estimate' is displayed in red colored font.

• Or if you want to create the custom field for invoice, then click on 'Invoice'.

• Enter the custom field name as shown in the images above.
• Click on the 'Save' button.

These custom fields will now be available for all the estimates/invoices that you create. In the case of the above example, the custom field 'Delivery Date' will appear when you create a new invoice. Refer image below.

How to I display the custom fields on the printed invoice/estimate?.

Once custom fields are created, for them to appear on the estimate/invoice, ensure to include the custom field (CF) placeholders on the template. The placeholder can be selected from the drop down menu as shown in the image below. The placeholder for custom field is %CustomLabel1%

Similarly, for the custom field value (date entered for delivery), the placeholder is %CustomValue1%, as shown in the image below.

Copy the placeholder and paste it anywhere in the template editor as shown in the image below. After making the necessary changes, save the template. From now, the custom fields will appear in the newly created invoices.

Settings >> Preferences >> Invoice Templates >> New Template >> Paper Size (A4/Letter)