Quote:
Which is the best coding language for this?
The one you know ... which judging by your tags is either PHP or Python. Any other language choice will necessitate your learning the language and the framework in which it works, as well as how to integrate that into your existing code base.
But I'd think rather more carefully before I even started on that - there are some very strange design choices in there, such as the apparent use of a PDF file as a database which is a somewhat esoteric design decision, particularly in a multiuser environment ...