Is a good starting point to understand how PDF's are generated by frontaccounting. It is very hard to understand the coding of these files..but if you spend a good amount of time (and you are a very good programmer) you might end up decoding how you can manipulate them to your needs.
I would say the three major files you need to look for are:
This is the first overlay that defines the horizontal lines and columns...on its own.. its empty..just the border lines and the rectangles you see on an invoice for example.I would call it the report empty overlay.
This is what what document data you need included within these line and boxes but not the data itself (within the above template).
3) reporting/repXXX.php are the the php coding that extracts that data using SQL queries to place the data within the above two files. i.e rep107.php for invoice, rep111.php for quotes .....etc.