1. Get New API Keys

If you want to have different pdf layout for each store and customer group, at less you need to have 2 API Keys of Easy PDF Invoice extension. You will need to pay for new API keys. In order to buy more API Keys, from your customer dashboard click to Upgrade button (see image below).

New modal window is displayed.In this new window you will see all available package for API Key.

Select the package would you like then click add to cart button.

Note that you will not be able to buy more API Keys if you are using the Free package of Easy PDF Invoice extension. 

After you process checkout you can add more API keys.

2. Setting the Easy PDF Invoice extension

So in example i have 2 API Keys now i will use these API Keys to set up the Easy PDF Invoice Extension.

From your Admin Panel of your magento installation, go to the menu Easy PDF -> Manage API Keys

Click to Add New button

Here you can select the option Store View and Customer Groups to make the API Key is used for that store views and customer groups.

After fill the form click to save button to store new API key to database.

Do the same thing with other API Keys which you have.

After all try to print something ;-)