Yes, it's possible.
In order to do this you need to install an additional extension from magento connect:
http://www.magentocommerce.com/magento-connect/easy-pdf-invoice-custom-variables.html
NOTE THAT THIS ADDITIONAL EXTENSION CANNOT BE INSALLED WITHOUT Magento PDF Invoice Pro extension or Easy PDF Invoice extension.
After you installed the extension. Go to Easy PDF -> Manage Custom Variables
Click to add Variable button.
Variable Name: This name will be used in your pdf template.
Type: You can add attribute from Customer or Product
Attribute: the attribute which you want to add to pdf invoice.
After you save the variable you will get the implementation code.
Copy this code and add it to your PDF.
If you are using the item widget you can add the custom attribute from widget see more from this post: http://www.vnecoms.com/kbase/extension-pdf-invoice-pro/magento-add-thumbnail-image-to-pdf-invoice.html
