In Zoho Books, we want to save an Invoice, Packing List and other documents for each Purchase Order.  These documents will be generated from the Purchase Order screen by clicking on individual buttons (Invoice, Packing List, Other) and the 'custom function' should pick up the appropriate custom template and generate a pdf and save to that PO. We then can send this PO along with all the attached pdf to our vendor.

How can this be achieved through custom buttons and custom functions?  I know I can do this manually by selecting a custom template and generating a pdf and saving to my hard drive.  Then do the same for the other pdfs.  Then manually attach them to the PO.  This process is tedious and prone to errors.