Q:

Write on a PDF file programmatically

I'm looking for a way to write text on PDF file in my code. 
I started with load the pdf file in a UIWebView and I add UILabel to the UIScrollView of the UIWebView.  Is it the good way to write on it? 
How can I save it with the modifications?  

A:

There is built in API for parsing PDF's:
However, I am not sure whether it allows to save modifications. 
You may be interested to take a look at this question:
how to edit a PDF in objective-c? 
modify / edit a PDF
Edit PDF in iphone application
Alos, Look at following libraries (they are commercial):

PSPDFKit
iAnnotate

