To print two existing reports (invoice and delivery report) with a single custom button in Odoo 16, you can create a new button in the user interface and define a server action to handle the logic of generating and printing the reports. Here's a step-by-step guide:

1. Create a Server Action:

    Go to Settings and enable the Developer Mode.

    Navigate to Technical -> Actions -> Server Actions.

    Create a new server action:

        Action Type: ir.actions.server

        Name: Choose a name for your server action.

        Model: Select the model you want to associate the server action with (e.g., Sale Order, Invoice, or any relevant model).

        Execution Context: Current Record

2. Define the Python Code:

In the server action, you need to define Python code that will generate and print the reports. Below is a sample Python code that you can adapt:

python

# Sample Python Code for the server action

invoice_ids = record.invoice_ids.filtered(lambda inv: inv.state == 'posted')

delivery_ids = record.picking_ids.filtered(lambda picking: picking.state == 'done')

# Generate and print the Invoice report

invoice_report = record.env.ref('account.report_invoice').render_qweb_pdf(invoice_ids.ids)

# Save or attach the invoice_report PDF as needed

# Generate and print the Delivery Order report

delivery_report = record.env.ref('stock.report_deliveryorder').render_qweb_pdf(delivery_ids.ids)

# Save or attach the delivery_report PDF as needed

In this code, record represents the current record for which the button is clicked. Adjust the code according to your specific model and logic.

3. Create a New Button:

    Navigate to the model for which you want to add the button (e.g., Sale Order, Invoice, or any relevant model).

    In the model's form view, add a new button to trigger the server action.

    xml

    Replace your_server_action_name with the actual name of your server action.

4. Adjust Security Settings:

Make sure that the user or user group has the necessary access rights to execute the server action and access the reports.

5. Test:

Test the button by navigating to a record of the associated model and clicking on the newly created button. Verify that both reports (invoice and delivery) are generated and printed as expected.