Access the payment method / Customise the payment method information

To access the payment method, use the following code 

$this->getPdfHelper()->getOrder()->getPayment()->getMethod()

in the Pdf Customiser template files to access the payment method (in this case retrieving the payment code).

To customise the payment method information, the information to display in the pdf is usually supplied directly by the payment method. 

For the default payment methods the templates can be found here: app/design/adminhtml/default/default/template/payment/info/pdf.