The invoice model is the template of the how the invoice will appear when generated.  The available invoice models depend on the theme that is loaded for  the Prestashop installation.  The following tutorial will show you how to select a different invoice model with PrestaShop 1.5.

Picking a Different Invoice Model with PrestaShop 1.5

1. Login to the Administrator Dashboard as an Administrator
2. Go to the menu bar and hover over ORDERS, then click on the second item that appears in the drop-down menu, INVOICES.  Scroll down into the  PRINT PDF INVOICE options and until you see:
   
   
   
   
   
   Note that the checkbox to the left is only available when you have multishop options enabled and you have selected a particular shop. 
   
   Clik on the checkbox to activate the INVOICE MODEL field:
3. Choose an INVOICE MODEL by click on the drop down menu.  You will have multiple options for the invoice model based on the theme that you have chosen.
   
   You can also find the existing invoice models in the /pdf/ folder of your PrestaShop 1.5 installation.  Knowledge of HTML is required to be able to modify or create your own invoice models.
4. Select the SAVE button at the bottom of the screen in order to save your changes.

Invoice models are used to modify the look and feel of the generated invoices used by PrestaShop 1.5.  You can easily change it based on the theme you have selected, or with some knowledge of HTML create your own models for the report.