Is it possible to customise PDF generation when, eg, generating PDF Reports? Client is wanting to know if it is possible to append custom information to the PDF report, eg packaging information and returns information which they are using for packing slips with client orders.
To the best of my knowledge, no. You can't customize the PDFs, because the current reports aren't really customizable. You would need to create an add-on for Store, like Custom Inventory Columns did or export the data and create custom reports on your desktop. You could possibly also create custom report layouts just using the Query Module in EE, and make them protected pages for your client.
Have you checked out PDF Press? http://devot-ee.com/add-ons/pdf-press
There are a few other options, too, including writing your own code if you're feeling adventurous.